Solid electrolyte, electrolyte layer and battery

ABSTRACT

A solid electrolyte having high electrical conductivity even in a low-temperature region is provided. A solid electrolyte containing a hexagonal perovskite-related compound, in which the compound is a compound represented by the following general formula (1), and an electrolyte layer and a battery using the solid electrolyte are disclosed. Ba7-αNb(4−x-y)Mo(1+x)MyO(20+z) (1), in the formula (1), M is a cation of at least one element; a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −1.1 or more and 1.1 or less, y represents a value of 0 or more and 1.1 or less, and z represents an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, provided that in the formula (1), |x|+y≥0.01 is satisfied.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a solid electrolyte used for a solid electrolyte layer such as a fuel cell, an electrolyte layer using the same, and a battery.

2. Description of the Related Art

Among fuel cells that have been studied in recent years, a solid oxide fuel cell (hereinafter, referred to as “SOFC”) has particularly high power generation efficiency, does not require a fuel-reforming device, and has excellent long-term stability, and therefore, the SOFC has a possibility of being widely applied to home use and business use, and is attracting attention.

The SOFC is configured to include a solid electrolyte-electrode laminate provided with fuel and air electrodes on both sides of the solid electrolyte layer. Yttria-stabilized zirconia (ZrO₂—Y₂O₃) (hereinafter, referred to as “YSZ”) is known as an oxide ion (O²⁻) conductive ceramic for the solid electrolyte layer used in SOFC.

Other examples of solid electrolytes used in SOFC include compounds with high electrical conductivity, for example, compounds with high ion conductivity that conduct ions such as oxide ions (O²⁻) and protons (H⁺).

Japanese Patent No. 6448020 discloses a crystalline inorganic compound capable of conducting at least one carrier selected from the group consisting of anions, cations, protons, electrons, and holes.

S. Fop, “Novel oxide ion conductors in the hexagonal perovskite family,” Bl. Ethos. 701786 (https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.701786) discloses Ba₇Nb₄MoO₂₀, which is a hexagonal perovskite-related compound having high ion conductivity (σ).

A conventional SOFC using YSZ as a solid electrolyte needs to be operated at a high temperature in order to obtain sufficient performance. The reason for this is that YSZ requires a high temperature of approximately 700° C. or more in order to ensure the oxide ion conductivity necessary for the battery. Operating a battery at a high temperature of 700° C. or more requires an environment and space in which the battery can be operated, other devices for keeping the battery at a high temperature and shutting off or cooling the battery so that other environments do not have a high temperature, and the like.

It is expected that if SOFC can be operated at low temperatures, the restriction for operating at a high temperature described above will be reduced, and the usefulness of SOFC will be significantly increased. It is also expected that the range of application of solid electrolytes other than SOFC will be greatly expanded because they can be operated at a low temperature. Therefore, a solid electrolyte having high electrical conductivity at a low temperature is strongly desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid electrolyte having high electrical conductivity even in a low-temperature region, and an electrolyte layer and a battery using the solid electrolyte.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention has the following aspects.

[1] A solid electrolyte containing a hexagonal perovskite-related compound, in which the compound is a compound represented by the following general formula (1):

Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (1)

in the formula (1), M is a cation of at least one element selected from the group consisting of Ag, Al, At, Au, Be, Bi, Br, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, I, In, Ir, La, Li, Lu, Mg, Mn, Na, Nb, Nd, Ni, Np, Os, P, Pb, Pd, Po, Pr, Pt, Pu, Re, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Tc, Te, Ti, Tl, Tm, U, V, W, Xe, Y, Yb, Zn, and Zr; and α represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −1.1 or more and 1.1 or less, y represents a value of 0 or more and 1.1 or less, and z represents an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, provided that in the formula (1), |x|+y≥0.01 is satisfied.

[2] A solid electrolyte containing a hexagonal perovskite-related compound, in which the compound is a compound represented by the following general formula (2):

Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (2),

in the formula (2), M is a cation of at least one element selected from the group consisting of W, V, Cr, Mn, Ge, Si, and Zr; and a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −1.1 or more and 1.1 or less, y represents a value of 0 or more and 1.1 or less and satisfying |x|+y≥0.01, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less.

[3] A solid electrolyte containing a hexagonal perovskite-related compound, in which the compound is a compound represented by any of the following general formulas (3) to (13):

Ba₇Nb_((4−x))Mo_((1+x))O_((20+z))  (3),

in the formula (3), x represents a value of −1.1 or more and −0.01 or less or 0.01 or more and 1.1 or less, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less;

Ba₇Nb_((4−y))MoM_(y)O_((20+z))  (4),

in the formula (4), M is a cation of at least one element selected from the group consisting of V, Mn, Ge, Si, and Zr; and y represents a value of 0.01 or more and 1.1 or less, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less];

Ba₇Nb₄Mo_((1−y))M_(y)O_((20+z))  (5),

in the formula (5), M is a cation of at least one element selected from the group consisting of V and Mn; and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less;

Ba₇Nb_((4−y))MoCr_(y)O_((20+z))  (6),

in the formula (6), z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less;

Ba₇Nb_((4−y))MoW_(y)O_((20+z))  (7),

in the formula (7), z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less;

Ba₃W_((1−x))V_((1+x))O_((8.5+z))  (8),

in the formula (8), x represents a value of −0.8 or more and 0.2 or less, z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less;

Ba₃Mo_((1−x))Ti_((1+x))O_((8+z))  (9),

in the formula (9), x represents a value of −0.3 or more and 0.1 or less, z is an oxygen non-stoichiometry and represents a value of −0.1 or more and 0.3 or less;

Ba₇Ca₂Mn₅O_((20+z))  (10),

in the formula (10), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less;

Ba_(2.6)Ca_(2.4)La₄Mn₄O_((19+z))  (11),

in the formula (11), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less;

La₂Ca₂MnO_((7+z))  (12),

in the formula (12), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less; and

Ba₅M₂Al₂ZrO_((13+z))  (13),

in the formula (13), M represents any of Gd, Dy, Ho, Er, Tm, Yb, or Lu; and z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less.

[4] The solid electrolyte according to [1] or [2], in which x is 0.06 or more and 0.30 or less.

[5] The solid electrolyte according to [3], in which the compound is a compound represented by the general formula (3), and x is 0.06 or more and 0.30 or less.

[6] The solid electrolyte according to [4] or [5], in which x is 0.19 or more and 0.21 or less.

[7] The solid electrolyte according to [2], in which in the compound, an a-axis length, a b-axis length, a c-axis length (Å), an α-angle, a β-angle, and a γ-angle (o) of a lattice constant are 5.35<a<6.56, 5.35<b<6.56, 15.14<c<18.52, 89<α<91, 89<β<91, and 119<γ<121, for the formula (2), respectively.

[8] The solid electrolyte according to [3], in which in the compound, an a-axis length, a b-axis length, a c-axis length (Å), an α-angle, a β-angle, and a γ-angle (o) of a lattice constant are in the numerical range of 5.35<a<6.56, 5.35<b<6.56, 15.14<c<18.52, 89<α<91, 89<β<91, and 119<γ<121, for the formulas (3) to (7), 5.23<a<6.4, 5.23<b<6.4, 18.96<c<23.19, 89<α<91, 89<β<91, and 119<γ<121,for the formula (8), 5.34<a<6.54, 5.34<b<6.54, 19.12<c<23.39, 89<α<91, 89<β<91, and 119<γ<121, for the formula (9), 5.23<a<6.41, 5.23<b<6.41, 46.23<c<56.51, 89<α<91, 89<β<91, and 119<γ<121, for the formula (10), 8.85<a<10.83, 5.11<b<6.26, 14.07<c<17.21, 89<α<91, 100<β<104, and 89<γ<91, for the formula (11), 5.05<a<6.19, 5.05<b<6.19, 15.57<c<19.03, 89<α<91, 89<β<91, and 119<γ<121, for the formula (12), and 5.35<a<6.55, 5.35<b<6.55, 22.23<c<27.18, 89<α<91, 89<β<91, and 119<γ<121, for the formula (13), respectively.

[9] The solid electrolyte according to any one of [1] to [8], in which the solid electrolyte is a solid electrolyte used as an oxide ion (O²⁻) conductor and is used under a temperature condition of 300 to 1200° C.

[10] The solid electrolyte according to any one of [1] to [9], in which the solid electrolyte has an electrical conductivity represented by log [σ(Scm⁻¹)] of −7 or more when measured at 300° C.

[11] The solid electrolyte according to any one of [1] to [10], in which the solid electrolyte is a solid oxide fuel cell (SOFC), a sensor, a battery, an electrode, an electrolyte, an oxygen concentrator, an oxygen separation membrane, an oxygen permeation membrane, an oxygen pump, a catalyst, a photocatalyst, an electric/electronic/communication device, an energy/environment-related device, or an optical device.

[12] The solid electrolyte according to any one of [1] to [11], in which the solid electrolyte is used for an electrolyte layer used in a solid oxide fuel cell (SOFC), a sensor, an oxygen concentrator, an oxygen separation membrane, an oxygen permeation membrane, or an oxygen pump.

[13] An electrolyte layer containing the solid electrolyte according to any one of [1] to [12].

[14] A battery including the electrolyte layer containing the solid electrolyte according to [13].

[15] The battery according to [14], in which the solid electrolyte is a solid oxide fuel cell (SOFC).

The present embodiment also has the following other aspects.

[1A] A solid electrolyte containing a hexagonal perovskite-related compound, in which the compound is a compound represented by the following general formula (1):

Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (1),

in the formula (1), M is a cation of at least one element selected from the group consisting of Ag, Al, At, Au, Be, Bi, Br, Cd, Co, Cr, Cu, Fe, Ga, Ge, Hf, Hg, I, In, Ir, Li, Mg, Mn, Mo, Nb, Ni, Np, Os, P, Pb, Pd, Po, Pt, Pu, Re, Rh, Ru, S, Sb, Sc, Se, Si, Sn, Ta, Tb, Tc, Te, Ti, Tl, U, V, W, Xe, Zn, and Zr; and a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −0.15 or more and 0.01 or less or 0.01 or more and 0.35 or less, y represents a value of 0.01 or more and 0.35 or less, and z is an oxygen non-stoichiometry and represents a value of −0.2 or more and 0.2 or less.

[2A] A solid electrolyte containing a hexagonal perovskite-related compound, in which the compound is a compound represented by the following general formula (2):

Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (2),

in the formula (2), M is a cation of at least one element selected from the group consisting of W, V, Cr, Ge, Si, and Zr; and a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −0.15 or more and 0.01 or less or 0.01 or more and 0.35 or less, y represents a value of 0.01 or more and 0.35 or less, and z is an oxygen non-stoichiometry and represents a value of −0.2 or more and 0.2 or less.

[3A] A solid electrolyte containing a hexagonal perovskite-related compound, in which the compound is a compound represented by any of the following general formulas (3) to (6):

Ba₇Nb_((4−x))Mo_((1+x))O_((20+z))  (3),

in the formula (3), x represents a value of −0.15 or more and −0.01 or less or 0.01 or more and 0.20 or less, and z is an oxygen non-stoichiometry and represents a value of −0.2 or more and 0.2 or less;

Ba₇Nb_((4−y))MoM_(y)O_((20+z))  (4),

in the formula (4), M is a cation of at least one element selected from the group consisting of W, V, Ge, Si, and Zr; and y represents a value of 0.01 or more and 0.2 or less, and z is an oxygen non-stoichiometry and represents a value of −0.2 or more and 0.2 or less;

Ba₇Nb₄Mo_((1−y))V_(y)O_((20+z))  (5),

in the formula (5), z is an oxygen non-stoichiometry and represents a value of −0.2 or more and 0.2 or less, and y represents a value of 0.01 or more and 0.2 or less;

Ba₇Nb_((4−y))MoCr_(y)O_((20+z))  (6),

in the formula (6), z is an oxygen non-stoichiometry and represents a value of −0.2 or more and 0.2 or less, and y represents a value of 0.01 or more and 0.35 or less;

[4A] The solid electrolyte according to any one of [1A] to [3A], in which x is 0.06 or more and 0.12 or less.

[5A] The solid electrolyte according to [4A], in which x is 0.09 or more and 0.11 or less.

[6A] The solid electrolyte according to any one of [1A] to [5A], in which in the compound, an a-axis length, a b-axis length, a c-axis length (Å), an α-angle, a β-angle, and a γ-angle (o) of a lattice constant are in the numerical range of 5.83<a<6.08, 5.83<b<6.08, 16.4<c<17.17, 89<α<91, 89<β<91, and 119<γ<121, respectively.

[7A] The solid electrolyte according to any one of [1A] to [6A], in which the solid electrolyte has an electrical conductivity represented by log [σ(Scm⁻¹)] of −6.2 or more when measured at 300° C.

Advantageous Effects of Invention

According to the present invention, a solid electrolyte having high electrical conductivity even in a low-temperature region, and an electrolyte layer and a battery using the solid electrolyte can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing an X-ray diffraction (XRD) pattern of Test Example 1 of the present example.

FIG. 2 is a graph showing the XRD pattern of Test Example 2 of the present example.

FIG. 3 is a graph showing the XRD pattern of Test Example 3 of the present example.

FIG. 4 is a graph showing the XRD pattern of Test Example 4 of the present example.

FIG. 5 is a graph showing the XRD pattern of Test Example 5 of the present example.

FIG. 6 is a graph showing the XRD pattern of Test Example 6 of the present example.

FIG. 7 is a graph showing the XRD pattern of Test Example 7 of the present example.

FIG. 8 is a graph showing the XRD pattern of Test Example 8 of the present example.

FIG. 9 is a graph showing the XRD pattern of Test Example 9 of the present example.

FIG. 10 is a graph showing the XRD pattern of Test Example 10 of the present example.

FIG. 11 is a graph showing the XRD pattern of Test Example 11 of the present example.

FIG. 12 is a graph showing the XRD pattern of Test Example 12 of the present example.

FIG. 13 is a graph showing the XRD pattern of Test Example 13 of the present example.

FIG. 14 is a graph showing the XRD pattern of Test Example 14 of the present example.

FIG. 15 is a graph showing the XRD pattern of Test Example 15 of the present example.

FIG. 16 is a graph showing the XRD pattern of Test Example 16 of the present example.

FIG. 17 is a graph showing the XRD pattern of Test Example 17 of the present example.

FIG. 18 is a graph showing the XRD pattern of Test Example 18 of the present example.

FIG. 19 is a graph showing the XRD pattern of Test Example 19 of the present example.

FIG. 20 is a graph showing the XRD pattern of Test Example 20 of the present example.

FIG. 21 is a graph showing the XRD pattern of Test Example 21 of the present example.

FIG. 22 is a graph showing a comparison of the electrical conductivity of Test Example 1 and Test Example 6 of the present example and YSZ.

FIG. 23 is a graph showing the electrical conductivity of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) in which the excess amount x of Mo in Test Examples of the present example is 0.02 to 0.10. For comparison, this graph also shows the electrical conductivity of Ba₇Nb₄MoO₂₀ in which the excess amount x of Mo of Test Examples of the present example is 0.0.

FIG. 24 is a graph showing the electrical conductivity of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) in which the excess amount x of Mo in Test Examples of the present example is 0.10 to 0.18. For comparison, this graph also shows the electrical conductivity of Ba₇Nb₄MoO₂₀ in which the excess amount x of Mo of Test Examples of the present example is 0.0.

FIG. 25 is a graph showing electrical conductivity of Ba₇Nb_((4−y))MoM_(y)O_((20+z)) in which the doping amount y of cations of each element of Cr, W, V, Si, Ge, and Zr is 0.1 and Ba₇Nb₄Mo_((1−y))V_(y)O_((20+z)) in which the doping amount y of cations of V is 0.1 in Test Examples of the present example.

FIG. 26 is a graph showing the electrical conductivity of Ba₇Nb_((4−y))MoCr_(y)O_((20+z)) in which the doping amount y of Cr of Test examples of the present example is 0.10 to 0.30.

FIG. 27 is a graph showing the oxygen partial pressure dependence of electrical conductivity at 900° C. in Test Example 1 of the present example.

FIG. 28 is a graph showing the relationship between the electromotive force and the oxygen partial pressure of the oxygen concentration cell at 800° C. in Test Example 6 of the present example.

FIG. 29 is a graph showing the relationship between the electromotive force and the oxygen partial pressure of the oxygen concentration cell at 900° C. in Test Example 6 of the present example.

FIG. 30 shows the crystal structure of Ba₇Nb₄MoO₂₀ which is Test Example 22.

FIG. 31 is a graph showing the XRD patterns of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) of Test Examples 22 to 27.

FIG. 32 shows XRD measurement charts of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) for Test Examples 28 to 37 with different compositions.

FIG. 33(a) shows the conductivity of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) of Test Examples 22 to 27 in a temperature-dependent manner. FIG. 33(b) shows the conductivity of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) for Test Examples 28 to 35 having different compositions in a temperature-dependent manner.

FIG. 34 shows the conductivity of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) of Test Examples 22 to 35 at a certain temperature in a composition-dependent manner.

FIG. 35 is a graph showing the XRD patterns of Ba₇Nb_((4−y))MoCr_(y)O_((2+z)) of Test Examples 40 to 44 and 46.

FIG. 36 shows the conductivity of Ba₇Nb_((4−y))MoCr_(y)O_((20+z)) of Test Examples 40 to 44 and 46 in a temperature-dependent manner.

FIG. 37 shows the conductivity of Ba₇Nb_((4−y))MoCr_(y)O_((2+z)) of Test Examples 22, 40 to 44, and 46 in a composition-dependent manner.

FIG. 38 is a graph showing the XRD patterns of Ba₇Nb_((4−y))MoW_(y)O_((20+z)) of Test Examples 52 to 58 and 81 and 83.

FIG. 39 shows the total electrical conductivity of Test Examples 52 to 58, 81, 82 of Ba₇Nb_((4−y))MoW_(y)O_((20+z)) in a temperature-dependent manner.

FIG. 40 shows the total electrical conductivity of Ba₇Nb_((4−y))MoW_(y)O_((20+z)) of Test Examples 22, 52 to 58, 81, and 82 in a composition-dependent manner.

FIG. 41 is a graph showing the XRD patterns of Test Examples 38, 39, 45, 47 to 51.

FIG. 42 shows the electrical conductivity of Test Examples 38, 39, and 47 to 50 in a temperature-dependent manner.

FIG. 43 shows the crystal structure of a Ba₃WVO_(8.5)-based material of Test Examples 59 to 67.

FIG. 44 is a graph showing the XRD patterns of Ba₃W_((1−x))V_((1+x))O_((8.5+z)) of Test Examples 59 to 67.

FIG. 45 shows the electrical conductivity of Ba₃W_((1−x))V_((1+x))O_((8.5+z)) of Test Examples 59 to 67 in a temperature-dependent manner

FIG. 46 shows the electrical conductivity of Ba₃W_((1−x))V_((1+x))O_((8.5+z)) of Test Examples 59 to 67 in a composition-dependent manner.

FIG. 47 shows the oxygen partial pressure P (O₂) dependence of total electrical conductivity for Ba₃W_(1.6)V_(0.4)O_(8.8) of Test Example 66.

FIG. 48 shows the conductivity of Ba₃W_(1.6)V_(0.4)O_(8.8) of Test Example 66 in dry air and in moist air in a temperature-dependent manner.

FIG. 49 shows the crystal structure of Ba₃MoTIO₈ of Test Example 68. Ba₃Mo_((1−x))Ti_((1+x))O_((8+z)) of Test Examples 69 and 70 also have a similar crystal structure.

FIG. 50 is a graph showing the XRD patterns of Ba₃Mo_((1−x))Ti_((1+x))O_((8+z)) of Test Examples 68 to 70.

FIG. 51 shows the electrical conductivity of Ba₃Mo_((1−x))Ti_((1+x))O_((8+z)) of Test Examples 68 to 70 in a temperature-dependent manner.

FIG. 52 shows the P (O₂) dependence of total electrical conductivity for Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) of Test Example 69.

FIG. 53 shows the crystal structure of Ba₇Ca₂Mn₅O₂₀ of Test Example 71.

FIG. 54 is a graph showing the XRD pattern of Ba₇Ca₂Mn₅O₂₀ of Test Example 71.

FIG. 55 shows the total electrical conductivity of Ba₇Ca₂Mn₅O₂₀ of Test Example 71 in a temperature-dependent manner.

FIG. 56 shows the crystal structure of Ba₂₆Ca₂₄La₄Mn₄O₁₉ of Test Example 72.

FIG. 57 is a graph showing the XRD pattern of Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ of Test Example 72.

FIG. 58 shows the total electrical conductivity of Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ of Test Example 72 in a temperature-dependent manner.

FIG. 59 shows the crystal structure of La₂Ca₂MnO₇ of Test Example 73.

FIG. 60 is a graph showing the XRD pattern of La₂Ca₂MnO₇ of Test Example 73.

FIG. 61 shows the crystal structure of a Ba₅M₂Al₂ZrO₁₃-based material of Test Examples 74 to 80.

FIG. 62 is a graph showing the XRD patterns of Ba₅M₂Al₂ZrO₁₃ of Test Examples 74 to 80.

FIG. 63 shows the total electrical conductivity of Ba₅M₂Al₂ZrO₁₃ of Test Examples 74 to 80 in a temperature-dependent manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a solid electrolyte, an electrolyte layer, and a battery according to the present invention will be described with reference to embodiments. However, the present invention is not limited to the following embodiments.

Solid Electrolyte

A solid electrolyte of the present embodiment contains a hexagonal perovskite-related compound that includes a compound represented by a specific general formula described later. Here, the solid electrolyte is a material through which ions are conducted, and also includes a material through which both ions and (protons, electrons or holes thereof) are conducted. The hexagonal perovskite-related compound in the present embodiment is a compound having a layered structure containing a hexagonal perovskite unit or a compound having a similar structure.

The hexagonal perovskite-related compound in the solid electrolytes of the present embodiment has a composition in which the Nb concentration or the Mo concentration is increased or decreased and/or the concentration of one or more cation-forming elements is increased with respect to conventionally known Ba₇Nb₄MoO₂₀. The cation-forming element described above is preferably at least one element selected from the group consisting of Ag, Al, At, Au, Be, Bi, Br, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, I, In, Ir, La, Li, Lu, Mg, Mn, Na, Nb, Nd, Ni, Np, Os, P, Pb, Pd, Po, Pr, Pt, Pu, Re, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Tc, Te, Ti, Tl, Tm, U, V, W, Xe, Y, Yb, Zn, and Zr, and more preferably at least one element selected from the group consisting of W, V, Cr, Mn, Ge, Yb, Zn, and Zr.

Specifically, the solid electrolyte of the present embodiment contains a hexagonal perovskite-related compound represented by any of the following general formulas (1) to (13).

Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (1),

in the formula (1), M is a cation of at least one element selected from the group consisting of Ag, Al, At, Au, Be, Bi, Br, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, I, In, Ir, La, Li, Lu, Mg, Mn, Na, Nb, Nd, Ni, Np, Os, P, Pb, Pd, Po, Pr, Pt, Pu, Re, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Tc, Te, Ti, Tl, Tm, U, V, W, Xe, Y, Yb, Zn, and Zr; and a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −1.1 or more and 1.1 or less, y represents a value of 0 or more and 1.1 or less, and z represents an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, provided that in the formula (1), |x|+y≥0.01 is satisfied.

Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (2),

in the formula (2), M is a cation of at least one element selected from the group consisting of W, V, Cr, Mn, Ge, Si, and Zr; and a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −1.1 or more and 1.1 or less, y represents a value of 0 or more and 1.1 or less and satisfying |x|+y≥0.01, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less.

Ba₇Nb_((4−x))Mo_((1+x))O_((20+z))  (3),

in the formula (3), x represents a value of −1.1 or more and −0.01 or less or 0.01 or more and 1.1 or less, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less.

Ba₇Nb_((4−y))MoM_(y)O_((20+z))  (4),

in the formula (4), M is a cation of at least one element selected from the group consisting of V, Mn, Ge, Si, and Zr; and y represents a value of 0.01 or more and 1.1 or less, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less.

Ba₇Nb₄Mo_((1−y))M_(y)O_((20+z))  (5),

in the formula (5), M is a cation of at least one element selected from the group consisting of V and Mn; and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less.

Ba₇Nb_((4−y))MoCr_(y)O_((20+z))  (6),

in the formula (6), z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less].

Ba₇Nb_((4−y))MoW_(y)O_((20+z))  (7),

in the formula (7), z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less].

In the formulas (1), (2), and (3), x is preferably 0.01 or more and 0.34 or less, more preferably 0.18 or more and 0.22 or less, and particularly preferably 0.19 or more and 0.21 or less. When x is the above value, particularly a value close to 0.20, the electrical conductivity at a low temperature becomes particularly high.

In the formulas (1) and (2), y is preferably 0.06 or more and 0.24 or less, more preferably 0.08 or more and 0.22 or less, and particularly preferably 0.09 or more and 0.21 or less. When y is the above value, particularly a value of 0.1 or more and 0.2 or less, the electrical conductivity at a low temperature becomes particularly high.

In the formulas (4) and (5), y is preferably 0.06 or more and 0.14 or less, more preferably 0.08 or more and 0.12 or less, and particularly preferably 0.09 or more and 0.11 or less. When y is the above value, particularly a value close to 0.10, the electrical conductivity at a low temperature becomes particularly high.

In the formulas (6), y is preferably 0.16 or more and 0.24 or less, more preferably 0.18 or more and 0.22 or less, and particularly preferably 0.19 or more and 0.21 or less. When y is the above value, particularly a value close to 0.20, the electrical conductivity at a low temperature becomes particularly high.

In the formulas (7), y is preferably 0.11 or more and 0.19 or less, more preferably 0.13 or more and 0.17 or less, and particularly preferably 0.14 or more and 0.16 or less. When y is the above value, particularly a value close to 0.15, the electrical conductivity at a low temperature becomes particularly high.

It is also preferable that Ba₃W_((1−x))V_((1+x))O_((8.5+z))  (8),

in the formula (8), x is preferably −0.8 or more and 0.2 or less, more preferably −0.64 or more and −0.56 or less, more preferably −0.62 or more and 0.58 or less, and more preferably −0.61 or more and −0.59 or less; when x is a value particularly close to −0.60, the electrical conductivity at a low temperature becomes particularly high; and z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less be satisfied.

It is also preferable that Ba₃Mo_((1−x))Ti_((1+x))O_((8+z))  (9),

in the formula (9), x is preferably −0.3 or more and 0.1 or less, more preferably −0.14 or more and −0.06 or less, more preferably −0.12 or more and 0.08 or less, and more preferably −0.11 or more and −0.09 or less; when x is a value particularly close to −0.10, the electrical conductivity at a low temperature becomes particularly high; and z is an oxygen non-stoichiometry and represents a value of −0.1 or more and 0.3 or less be satisfied.

It is also preferable that Ba₇Ca₂Mn₅O_((20+z))  (10),

in the formula (10), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less be satisfied.

It is also preferable that Ba_(2.6)Ca_(2.4)La₄Mn₄O_((19+z))  (11),

in the formula (11), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less be satisfied.

It is also preferable that La₂Ca₂MnO_((7+z))  (12),

in the formula (12), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less be satisfied.

It is also preferable that Ba₅M₂Al₂ZrO_((13+z))  (13),

in the formula (13), M represents any of Gd, Dy, Ho, Er, Tm, Yb, or Lu; and z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less be satisfied.

Among the hexagonal perovskite-related compounds of the solid electrolytes of the present embodiment, preferred examples thereof include those in which the Mo/Nb ratio is increased with respect to conventionally known Ba₇Nb₄MoO₂₀. That is, when x in the general formula (3) is the excess amount x of Mo, x is preferably a positive value, specifically a value of 0.01 or more and 0.50 or less, more preferably a value of 0.01 or more and 0.34 or less, still more preferably 0.18 or more and 0.22 or less, and particularly preferably 0.19 or more and 0.21 or less. Specifically, when the excess amount x of Mo is 0.20 with respect to Ba₇Nb₄MoO₂₀, particularly high electrical conductivity can be obtained.

In addition, the excess amount x of Mo may be appropriately adjusted within a range of −1.1 or more and 1.1 or less depending on the raw materials used and the adjustment process so as to be easily produced. For example, the excess amount x may be a value of 0.01 or more and 0.20 or less, or may be a value of 0.09 or more and 0.11 or less, and even at these values, high conductivity can be obtained. Further, for example, when the excess amount x of Mo is 0.10 with respect to Ba₇Nb₄MoO₂₀, high conductivity can be obtained.

Further, it may be selected from the above formulas (1) to (13) excluding Ba₃W_((1−x))V_((1+x))O_((8.5+z)) (x=−0.75, −0.60, −0.50, −0.40, −0.25, −0.10, −0.05, 0.0, 0.05, 0.10) and Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉.

Further, in the hexagonal perovskite-related compound in the present embodiment, an a-axis length, a b-axis length, a c-axis length (Å), an α-angle, a β-angle, and a γ-angle (o) of the lattice constant are preferably in the numerical range of 5.35<a<6.56, 5.35<b<6.56, 15.14<c<18.52, 89<α<91, 89<β<91, and 119<γ<121, for the formulas (2) to (7), 5.23<a<6.4, 5.23<b<6.4, 18.96<c<23.19, 89<α<91, 89<β<91, and 119<γ<121, for the formula (8), 5.34<a<6.54, 5.34<b<6.54, 19.12<c<23.39, 89<α<91, 89<β<91, and 119<γ<121, for the formula (9), 5.23<a<6.41, 5.23<b<6.41, 46.23<c<56.51, 89<α<91, 89<β<91, and 119<γ<121, for the formula (10), 8.85<a<10.83, 5.11<b<6.26, 14.07<c<17.21, 89<α<91, 100<β<104, and 89<γ<91, for the formula (11), 5.05<a<6.19, 5.05<b<6.19, 15.57<c<19.03, 89<α<91, 89<β<91, and 119<γ<121, for the formula (12), and 5.35<a<6.55, 5.35<b<6.55, 22.23<c<27.18, 89<α<91, 89<β<91, and 119<γ<121, for the formula (13), respectively. Here, the lattice constant is a constant that defines the shape and size of the unit lattice of the present embodiment. α is an angle formed by the b-axis and the c-axis, β is an angle formed by the a-axis and the c-axis, and γ is an angle formed by the a-axis and the b-axis. The lattice constant can be obtained by using an XRD (X-ray diffraction) pattern in the present embodiment. The theoretically possible value of the lattice constant can also be obtained by structural optimization by density functional theory (DFT) calculation.

A compound having this lattice constant has the effect of having high electrical conductivity at low temperatures.

In the present embodiment, it is assumed that a compound having each of the above-described conditions provides effective electrical conductivity (oxide ion conductivity) when used as an oxide ion (O²⁻) conductor or a solid electrolyte. Oxide ion (O²⁻) conductors are compounds in which electricity is conducted by conduction (movement) of oxide ions. Further, the solid electrolyte using the compound of the present embodiment is preferably used under a temperature condition of 300 to 1200° C., more preferably used under a temperature condition of 300 to 1000° C., still more preferably used at 300° C. or more and less than 700° C., and particularly preferably used at 300 to 600° C. By using the solid electrolyte under these temperature conditions, it is possible to operate at a lower temperature than the conventional SOFC, so that there are few restrictions on the equipment and arrangement required for the operation, and a wide range of applications can be obtained.

The solid electrolyte using the compound of the present embodiment can be operated at a temperature exceeding 600° C. as in a conventional SOFC.

When the electrical conductivity of the solid electrolyte of the present embodiment is measured at about 300° C., the electrical conductivity represented by log [σ(Scm⁻¹)] is preferably −7 or more, more preferably higher than −5.0, and particularly preferably −3.5 or more. Since the electrical conductivity at 300° C. is sufficiently high, the electrical conductivity is high at a low temperature, and it can be particularly preferably used for a battery or other device operating at a low temperature.

Solid Electrolyte Layer

Further, the solid electrolyte of the present embodiment can be used as a solid electrolyte layer by being formed in a layer shape or being formed so as to be included in a layered structure. The solid electrolyte layer may conductor another ion conductor or the like in addition to the solid electrolyte of the present embodiment. In order for a battery or the like using the solid electrolyte of the present embodiment to exhibit effective electrical conductivity and to effectively operate as a low-temperature operating battery described later in particular, it is preferable for the solid electrolyte layer to contain, for example, 50% by mass or more, preferably 70% by mass or more, of the solid electrolyte containing the hexagonal perovskite-related compound of the present embodiment.

Battery Containing Solid Electrolyte or Solid Electrolyte Layer

The solid electrolyte of the present embodiment, or the electrolyte layer containing the solid electrolyte, can be used for a battery containing the solid electrolyte. Of these, the solid electrolyte of the present embodiment can be particularly preferably used for a solid oxide fuel cell (SOFC) as described above.

The SOFC in the present embodiment means a battery in which all the electrodes and electrolytes constituting the battery are made of solid. In particular, the ionic conduction between the electrodes may be oxide ions.

The battery using the solid electrolyte in the present embodiment or the electrolyte layer containing the solid electrolyte can be particularly preferably used for a low-temperature operating battery. In the present embodiment, the low-temperature operating battery is a battery that operates at 300 to 1200° C., preferably 300 to 1000° C., more preferably 300 or more and less than 700° C., and particularly preferably 300 to 600° C., as described above.

The battery in the present embodiment includes, for example, an anode, a cathode, and the above-described solid electrolyte layer interposed therebetween. The cathode and the solid electrolyte may form an integrated cathode-solid electrolyte layer assembly.

Other Applications of Solid Electrolyte

Conventionally, perovskite-related compounds and solid electrolytes containing the perovskite-related compounds exhibit high ion conductivity, and thus are widely applied to batteries, sensors, ion concentrators, membranes used for ion separation, permeation, and the like, catalysts, and the like, and the solid electrolyte of the present embodiment can be applied in the same manner as these. For example, the solid electrolyte of the present embodiment can be used for other batteries, sensors, electrodes, electrolytes, oxygen concentrators, oxygen separation membranes, oxygen permeation membranes, oxygen pumps, catalysts, photocatalysts, electric/electronic/communication devices, energy/environment-related devices, and optical devices, in addition to the above-described solid oxide fuel cell (SOFC).

The solid electrolyte layer of the present embodiment described above can be used for a solid oxide fuel cell (SOFC), a sensor, an oxygen concentrator, an oxygen separation membrane, an oxygen permeation membrane, an oxygen pump, or the like.

The solid electrolyte of the present embodiment can be used as an electrolyte of a gas sensor, for example, as a sensor. A gas sensor, gas detector, or the like can be constituted by attaching a sensitive electrode corresponding to the gas to be detected on the electrolyte. For example, a carbon dioxide sensor can be obtained when a sensitive electrode containing carbonate is used, a NOx sensor can be obtained when a sensitive electrode containing a nitrate is used, and an SOx sensor can be obtained when a sensitive electrode containing sulfate is used. Further, by assembling the electrolytic cell, a collecting device or a decomposing device for NOx and/or SOx contained in exhaust gas can be constituted.

The solid electrolyte of the present embodiment can be used as an adsorbent or an adsorption-separation agent for ions or the like, various catalysts, or the like.

In the solid electrolyte of the present embodiment, various rare earths in the ion conductor may act as an activator forming a light emission center (color center). In this case, it can be used as a wavelength-changing material or the like.

The solid electrolyte of the present embodiment may also become a superconductor by doping with electron carriers or hole carriers.

Regarding the solid electrolyte of the present embodiment, it is also possible to fabricate an all-solid-state electrochromic element by, using the solid electrolyte as an ion conductor, attaching an inorganic compound or the like which is colored or discolored by insertion/desorption of conduction ions to the surface thereof, and forming a translucent electrode such as ITO thereon. By using this all-solid-state electrochromic element, it is possible to provide an electrochromic display having memory characteristics with reduced power consumption.

EXAMPLES Sample Synthesis—Test Examples 1 to 21

The compounds shown in “Composition” of Test Examples 1 to 21 in Table 1 were prepared by the solid-phase reaction method. In the composition shown in Table 1, the oxygen amount calculated from the electrically neutral condition is shown assuming that the oxidation number of Ba is +2, the oxidation number of Nb is +5, the oxidation number of Mo is +6, the oxidation number of oxygen O is −2, the oxidation number of W is +6, the oxidation number of V is +5, the oxidation number of Cr is +6, the oxidation number of Ge is +4, the oxidation number of Si is +4, and the oxidation number of Zr is +4, but the oxygen amount (20+z) is not limited to the values shown because the oxygen non-stoichiometry z depends on the cation molar ratio, temperature, oxygen partial pressure, synthesis method, and thermal history. BaCO₃, Nb₂O₅, MoO₃, WO₃, V₂O₅, Cr₂O₃, GeO₂, SiO₂, and ZrO₂ were used as starting materials. The starting materials were dried in advance in an electric furnace at 250 to 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for 30 minutes to 2 hours. The obtained mixture was calcined in the air at 900° C. for 10 to 12 hours using an electric furnace. The calcined mixture was repeatedly subjected to wet mixing and grinding using ethanol and dry mixing and grinding in an agate mortar for 30 minutes to 2 hours. The mixture was molded into cylindrical pellets having a diameter of 10 to 20 mm by pressurizing at 62 to 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1100° C. for 24 hours. As a result, pellets as a sintered body were obtained. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for 20 minutes by a grinder made of tungsten carbide (WC) and then ground for 30 minutes to 1 hour by an agate mortar.

For the compounds having the compositions of Test Examples 1 and 6, high-density samples were prepared by means of applying hydrostatic pressure once before sintering. On the other hand, a sample sintered without being subjected to hydrostatic pressure treatment before sintering is called a low-density sample. Assuming a theoretical density for each sample of 5.85 g/cm³, the following relative densities were calculated: 100×(density)/(theoretical density) %.

The high-density sample of Test Example 1 had a density of 5.2725 g/cm³ and a relative density of 90.1%.

The low-density sample of Test Example 1 had a density of 3.9659 g/cm³ and a relative density of 67.8%.

The high-density sample of Test Example 6 had a density of 5.5951 g/cm³ and a relative density of 95.6%.

The low-density sample of Test Example 6 had a density of 3.9165 g/cm³ and a relative density of 66.9%.

For each test example, XRD measurement was performed by a diffractometer Bruker D8. The obtained XRD pattern was indexed using DICVOL06 to obtain the lattice constant. The XRD pattern of Test Example 1 is shown in FIG. 1.

The results of XRD measurement of Test Examples 2 to 21 are also shown in FIGS. 2 to 21, respectively. The lattice constants were determined from the obtained XRD patterns. The lattice constants (a, b, c, α, β, γ) and the lattice volume V of Test Examples 1 to 21 are shown in Table 1.

TABLE 1 Crystal lattice Composition a[Å] b[Å] c[Å] α[°] β[°] γ[°] V[Å³] Test Example 1 Ba₇Nb₄MoO₂₀ 5.8602 5.8602 16.5311 90 90 120 491.72 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 5.8606 5.8606 16.5361 90 90 120 491.87 Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 5.8605 5.8605 16.5406 90 90 120 491.99 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 5.8599 5.8599 16.5298 90 90 120 491.57 Test Example 5 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 5.8598 5.8598 16.5288 90 90 120 491.50 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 5.8592 5.8592 16.5181 90 90 120 491.11 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 5.8601 5.8601 16.5315 90 90 120 491.65 Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 5.8608 5.8608 16.5339 90 90 120 491.83 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 5.8605 5.8605 16.5337 90 90 120 491.78 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 5.8604 5.8604 16.5347 90 90 120 491.79 Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 5.8585 5.8585 16.5038 90 90 120 490.56 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 5.8584 5.8584 16.5259 90 90 120 491.19 Test Example 13 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 5.8557 5.8557 16.5114 90 90 120 490.32 Test Example 14 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 5.8539 5.8539 16.5122 90 90 120 490.04 Test Example 15 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 5.8474 5.8474 16.4985 90 90 120 488.54 Test Example 16 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 5.8474 5.8474 16.5084 90 90 120 488.84 Test Example 17 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 5.8555 5.8555 16.5156 90 90 120 490.41 Test Example 18 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 5.8579 5.8579 16.5257 90 90 120 491.10 Test Example 19 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 5.8597 5.8597 16.5204 90 90 120 491.26 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 5.8557 5.8557 16.5206 90 90 120 490.59 Test Example 21 Ba₇Nb_(4.1)Mo_(0.9)O_(19.95) 5.8624 5.8624 16.5463 90 90 120 492.47

Measurement of Total Electrical Conductivity

The electrical conductivity of each test example in Table 1 excluding Test Example 21 was measured by the DC four-terminal method. After reducing the particle size of the sample prepared in the above (Sample Synthesis) using a ball-mill, the sample was molded into pellets having a 5 mm φ by uniaxial pressing and sintered to prepare a sample for conductivity measurement. Four platinum wires were wound around a sintered body for measuring total electrical conductivity by the DC four-terminal method, and platinum paste was applied on the platinum wires in order to bring the sample and the platinum wires into close contact with each other. In order to remove organic components contained in the platinum or gold paste, the paste was heated at 900° C. for 1 hour. The electrical conductivity measured for each test example is shown in Tables 2 to 9. In the composition shown in Tables 2 to 9, the oxygen amount calculated from the electrically neutral condition is shown assuming that the oxidation number of Ba is +2, the oxidation number of Nb is +5, the oxidation number of Mo is +6, the oxidation number of oxygen O is −2, the oxidation number of W is +6, the oxidation number of V is +5, the oxidation number of Cr is +6, the oxidation number of Ge is +4, the oxidation number of Si is +4, and the oxidation number of Zr is +4, but the oxygen amount (20+z) is not limited to the values shown because the oxygen non-stoichiometry z depends on the cation molar ratio, temperature, oxygen partial pressure, synthesis method, and thermal history.

TABLE 2 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 1 Ba₇Nb₄MoO₂₀ (high density) 408° C. −3.8 Test Example 1 Ba₇Nb₄MoO₂₀ (high density) 505° C. −3.3 Test Example 1 Ba₇Nb₄MoO₂₀ (high density) 605° C. −2.9 Test Example 1 Ba₇Nb₄MoO₂₀ (high density) 705° C. −2.6 Test Example 1 Ba₇Nb₄MoO₂₀ (high density) 804° C. −2.4 Test Example 1 Ba₇Nb₄MoO₂₀ (high density) 904° C. −2.3 Test Example 1 Ba₇Nb₄MoO₂₀ (low density) 307° C. −5.7 Test Example 1 Ba₇Nb₄MoO₂₀ (low density) 408° C. −4.7 Test Example 1 Ba₇Nb₄MoO₂₀ (low density) 509° C. −4 Test Example 1 Ba₇Nb₄MoO₂₀ (low density) 610° C. −3.4 Test Example 1 Ba₇Nb₄MoO₂₀ (low density) 709° C. −3 Test Example 1 Ba₇Nb₄MoO₂₀ (low density) 809° C. −2.7 Test Example 1 Ba₇Nb₄MoO₂₀ (low density) 908° C. −2.6 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 305° C. −4.9 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 406° C. −3.8 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 506° C. −3.1 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 608° C. −2.8 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 708° C. −2.7 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 808° C. −2.6 Test Example 2 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 908° C. −2.5

TABLE 3 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 307° C. −4.7 Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 410° C. −3.6 Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 510° C. −2.9 Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 610° C. −2.6 Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 710° C. −2.5 Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 809° C. −2.4 Test Example 3 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 909° C. −2.3 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 302° C. −5.2 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 406° C. −3.9 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 506° C. −3.2 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 607° C. −2.7 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 708° C. −2.5 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 808° C. −2.4 Test Example 4 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 905° C. −2.4 Test Example 4 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 306° C. −4.4 Test Example 5 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 408° C. −3.4 Test Example 5 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 510° C. −2.8 Test Example 5 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 609° C. −2.5 Test Example 5 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 709° C. −2.4 Test Example 5 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 809° C. −2.3 Test Example 5 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 908° C. −2.2

TABLE 4 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 280° C. −3.7 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 358° C. −3.2 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 457° C. −2.7 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 561° C. −2.3 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 658° C. −2.1 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 721° C. −2 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 840° C. −1.9 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 878° C. −1.9 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (high density) 307° C. −5.5 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (low density) 409° C. −4.4 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (low density) 509° C. −3.8 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (low density) 610° C. −3.2 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (low density) 710° C. −2.9 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (low density) 809° C. −2.7 Test Example 6 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) (low density) 909° C. −2.5 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 305° C. −5 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 406° C. −3.7 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 507° C. −3 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 607° C. −2.6 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 707° C. −2.4 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 808° C. −2.3 Test Example 7 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 908° C. −2.2

TABLE 5 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 308° C. −4.6 Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 408° C. −3.4 Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 508° C. −2.8 Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 608° C. −2.5 Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 708° C. −2.3 Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 808° C. −2.1 Test Example 8 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 907° C. −2.1 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 304° C. −4.5 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 406° C. −3.4 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 506° C. −2.7 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 607° C. −2.4 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 707° C. −2.2 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 807° C. −2.2 Test Example 9 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 906° C. −2.1 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 307° C. −4.3 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 408° C. −3.3 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 509° C. −2.7 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 610° C. −2.4 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 709° C. −2.3 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 809° C. −2.2 Test Example 10 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 908° C. −2.1

TABLE 6 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 306° C. −4.1 Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 409° C. −3.3 Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 508° C. −2.8 Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 608° C. −2.5 Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 707° C. −2.2 Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 808° C. −2 Test Example 11 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 907° C. −1.9 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 306° C. −5.4 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 409° C. −4.2 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 508° C. −3.5 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 608° C. −3.2 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 707° C. −3.2 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 806° C. −3.1 Test Example 12 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 908° C. −2.9 Test Example 13 Ba₇Nb_(3.9)V_(0.1)MoO₂₀ 304° C. −5.8 Test Example 13 Ba₇Nb_(3.9)V_(0.1)MoO₂₀ 405° C. −4.8 Test Example 13 Ba₇Nb_(3.9)V_(0.1)MoO₂₀ 506° C. −4.2 Test Example 13 Ba₇Nb_(3.9)V_(0.1)MoO₂₀ 607° C. −3.6 Test Example 13 Ba₇Nb_(3.9)V_(0.1)MoO₂₀ 707° C. −3.1 Test Example 13 Ba₇Nb_(3.9)V_(0.1)MoO₂₀ 807° C. −2.9 Test Example 13 Ba₇Nb_(3.9)V_(0.1)MoO₂₀ 908° C. −2.8

TABLE 7 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 14 Ba₇Nb_(3.9)Cr_(0.1)MoO_(20.05) 304° C. −5.5 Test Example 14 Ba₇Nb_(3.9)Cr_(0.1)MoO_(20.05) 402° C. −4.5 Test Example 14 Ba₇Nb_(3.9)Cr_(0.1)MoO_(20.05) 505° C. −3.6 Test Example 14 Ba₇Nb_(3.9)Cr_(0.1)MoO_(20.05) 605° C. −3 Test Example 14 Ba₇Nb_(3.9)Cr_(0.1)MoO_(20.05) 706° C. −2.6 Test Example 14 Ba₇Nb_(3.9)Cr_(0.1)MoO_(20.05) 807° C. −2.4 Test Example 14 Ba₇Nb_(3.9)Cr_(0.1)MoO_(20.05) 907° C. −2.3 Test Example 15 Ba₇Nb_(3.8)Cr_(0.2)MoO_(20.1) 309° C. −5 Test Example 15 Ba₇Nb_(3.8)Cr_(0.2)MoO_(20.1) 410° C. −3.7 Test Example 15 Ba₇Nb_(3.8)Cr_(0.2)MoO_(20.1) 509° C. −3 Test Example 15 Ba₇Nb_(3.8)Cr_(0.2)MoO_(20.1) 610° C. −2.6 Test Example 15 Ba₇Nb_(3.8)Cr_(0.2)MoO_(20.1) 710° C. −2.3 Test Example 15 Ba₇Nb_(3.8)Cr_(0.2)MoO_(20.1) 809° C. −2.2 Test Example 15 Ba₇Nb_(3.8)Cr_(0.2)MoO_(20.1) 908° C. −2.2 Test Example 16 Ba₇Nb_(3.7)Cr_(0.3)MoO_(20.15) 302° C. −4.6 Test Example 16 Ba₇Nb_(3.7)Cr_(0.3)MoO_(20.15) 401° C. −3.9 Test Example 16 Ba₇Nb_(3.7)Cr_(0.3)MoO_(20.15) 505° C. −3.1 Test Example 16 Ba₇Nb_(3.7)Cr_(0.3)MoO_(20.15) 607° C. −2.7 Test Example 16 Ba₇Nb_(3.7)Cr_(0.3)MoO_(20.15) 700° C. −2.4 Test Example 16 Ba₇Nb_(3.7)Cr_(0.3)MoO_(20.15) 803° C. −2.4 Test Example 16 Ba₇Nb_(3.7)Cr_(0.3)MoO_(20.15) 905° C. −2.5

TABLE 8 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 17 Ba₇Nb_(3.9)Ge_(0.1)MoO_(19.95) 303° C. −5.6 Test Example 17 Ba₇Nb_(3.9)Ge_(0.1)MoO_(19.95) 406° C. −4.7 Test Example 17 Ba₇Nb_(3.9)Ge_(0.1)MoO_(19.95) 506° C. −4 Test Example 17 Ba₇Nb_(3.9)Ge_(0.1)MoO_(19.95) 607° C. −3.5 Test Example 17 Ba₇Nb_(3.9)Ge_(0.1)MoO_(19.95) 707° C. −3.3 Test Example 17 Ba₇Nb_(3.9)Ge_(0.1)MoO_(19.95) 808° C. −3.1 Test Example 17 Ba₇Nb_(3.9)Ge_(0.1)MoO_(19.95) 908° C. −2.9 Test Example 18 Ba₇Nb_(3.9)Si_(0.1)MoO_(19.95) 309° C. −5.2 Test Example 18 Ba₇Nb_(3.9)Si_(0.1)MoO_(19.95) 409° C. −4.1 Test Example 18 Ba₇Nb_(3.9)Si_(0.1)MoO_(19.95) 510° C. −4.1 Test Example 18 Ba₇Nb_(3.9)Si_(0.1)MoO_(19.95) 610° C. −4 Test Example 18 Ba₇Nb_(3.9)Si_(0.1)MoO_(19.95) 709° C. −3.6 Test Example 18 Ba₇Nb_(3.9)Si_(0.1)MoO_(19.95) 809° C. −3.5 Test Example 18 Ba₇Nb_(3.9)Si_(0.1)MoO_(19.95) 908° C. −3.3

TABLE 9 Total electrical conductivity (=oxide ion conductivity) Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 19 Ba₇Nb_(3.9)Zr_(0.1)MoO_(19.95) 305° C. −6.2 Test Example 19 Ba₇Nb_(3.9)Zr_(0.1)MoO_(19.95) 404° C. −5.5 Test Example 19 Ba₇Nb_(3.9)Zr_(0.1)MoO_(19.95) 504° C. −4.6 Test Example 19 Ba₇Nb_(3.9)Zr_(0.1)MoO_(19.95) 606° C. −4 Test Example 19 Ba₇Nb_(3.9)Zr_(0.1)MoO_(19.95) 707° C. −3.6 Test Example 19 Ba₇Nb_(3.9)Zr_(0.1)MoO_(19.95) 807° C. −3.4 Test Example 19 Ba₇Nb_(3.9)Zr_(0.1)MoO_(19.95) 907° C. −3.3 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 305° C. −4.8 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 406° C. −3.7 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 506° C. −3 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 607° C. −2.7 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 707° C. −2.6 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 807° C. −2.5 Test Example 20 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 907° C. −2.4

From Tables 2 to 9, for all of Test Examples 2 to 20, the electrical conductivity represented by log [σ(Scm⁻¹)] in the temperature range of 280 to 909° C. was within the range of −7.0 to −1.0. In Test Examples 2 to 20, the electrical conductivity represented by log [σ(Scm⁻¹)] obtained by extrapolation from the electrical conductivity at 300° C. or the above data and FIG. 22 to is −6.2 or more. Therefore, for all of Test Examples 2 to 20, high electrical conductivity can be obtained at a low temperature. Further, the electrical conductivity at 300° C. is higher than −5.0 in Test Examples 2, 3, 5, 6 (high density), 8 to 11, 16, and 20. Of all the test examples, the test example having the highest electrical conductivity at around 300° C. described above is Test Example 6, and the value of the electrical conductivity log [σ(Scm⁻¹)] at 280° C. is −3.7. Although the electrical conductivity for Test Example 21 was not measured, it is considered that it exhibits electrical (ionic) conduction in the same manner as in Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) of Test Example 20.

FIG. 22 shows a graph (Arrhenius plot) in which log [σ(Scm⁻¹)] is plotted on the vertical axis and 1000 T⁻¹/K⁻¹ is plotted on the horizontal axis for the absolute temperature T obtained from the temperature of the table for each electrical conductivity CS of conventionally used YSZ (Comparative Example 1), Test Example 1 (Ba₇Nb₄MoO₂₀) (high density), and Test Example 6 (Ba₇Nb_(3.9)Mo_(1.1)O_(20.05)) (high density).

From FIG. 22, the electrical conductivity increases as the temperature rises. At 600° C., the electrical conductivity a of Test Example 6, in which the excess amount x of Mo was 0.10, was 5.5 times higher than the electrical conductivity of Ba₇Nb₄MoO₂₀ of Test Example 1, indicating that the electrical conductivity was improved by increasing the Mo amount.

In the conventional Test Example 1, the log [σ(Scm⁻¹)]=−2.7 at 600° C. In Test Example 6, in which the excess amount x of Mo was set to 0.10, the log [σ(Scm⁻¹)] was higher than those of YSZ and Test Example 1 at a temperature of 590° C. or less, indicating that the electrical conductivity was higher than that of a conventionally used electrolyte.

Further, FIG. 23 shows an Arrhenius plot of the electrical conductivity of Ba₇Nb₄MoO₂₀ in which the excess amount x of Mo is 0.02 to 0.10 in the general formula (7), and FIG. 24 shows an Arrhenius plot of the electrical conductivity of Ba₇Nb₄MoO₂₀ in which the excess amount x of Mo is 0.10 to 0.18. For comparison, FIGS. 23 and 24 also show the electrical conductivity of Ba₇Nb₄MoO₂₀ in which the excess amount x of Mo of Test Examples of the present example is 0.0. Test Examples 1 (high density, low density), 2, 3, 4, 5, 6 (high density, low density), 7, 8, 9, and 10 correspond to samples in which the excess amount x of Mo (x in Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) of the general formula (7)) is 0 (high density, low density), 0.02, 0.04, 0.06, 0.08, 0.10 (high density, low density), 0.12, 0.14, 0.16, and 0.18, respectively.

The electrical conductivity of Test Example 1 (x=0) and Test Example 6 (x=0.10) of the high-density sample is higher than that of the low-density sample at any temperature.

All of the samples in which the excess amount x of Mo is in the range of 0.02 to 0.18 (Test Examples 2 to 10) show higher electrical conductivity than the low-density sample of Ba₇Nb₄MoO₂₀ (Test Example 1) in which the excess amount x of Mo is 0. The high-density sample in which the excess amount x of Mo is 0.10 has the highest electrical conductivity, and high electrical conductivity is maintained even at a low temperature of about 300° C.

FIG. 25 shows an Arrhenius plot of the electrical conductivity of Ba₇Nb₄MoO₂₀ (y=0.10 in the general formulas (4) to (7)) in which the doping amount y of W, V (substituting part of Mo), V (substituting part of Nb), Cr, Si, Ge, and Zr is 0.1. Test Examples 11, 12, 13, 14, 17, 18, and 19 described above correspond to results of compounds doped with W (substituting part of Nb), V (substituting part of Mo), V, Cr, Ge, Si, and Zr (substituting part of Nb), respectively. Among these compounds, the compound doped with W has the highest electrical conductivity in all of the plotted temperature regions. In other Test Examples, the electrical conductivity of the compound doped with Cr and V (substituting part of Mo) is high at a high temperature, but the electrical conductivity of the compound doped with Si increases when 1000T⁻¹/K⁻¹ becomes 1.4 or more, that is, at a low temperature of approximately 441° C. or less.

Further, FIG. 26 shows an Arrhenius plot of the electrical conductivity of Ba₇Nb₄MoO₂₀ in which the doping amount y of Cr is 0.10 to 0.30 (Ba₇Nb_((4−y))MoCr_(y)O_((20+z)) in which y=0.10 to 0.30 in the general formula (10)). Test Examples 14, 15, and 16 described above correspond to samples having a doping amount y of 0.10, 0.20, and 0.30, respectively. The electrical conductivity of Ba₇Nb₄MoO₂₀ (y=0.10 to 0.30) in which the doping amount y of Cr is 0.10 to 0.30 is higher than that of Ba₇Nb₄MoO₂₀ at 800° C. or lower.

Oxygen Partial Pressure Dependence of Total Electrical Conductivity

For Test Example 1, the oxygen partial pressure dependence of total electrical conductivity was measured. Samples were prepared in the same manner as described above (measurement of total electrical conductivity). The oxygen partial pressure was controlled by using an oxygen O₂ gas, a nitrogen N₂ gas, and an N₂/H₂ mixed gas.

The oxygen partial pressure dependence of total electrical conductivity was measured at an oxygen partial pressure range of 3.5×10⁻²⁵ to 0.2 atm and 900° C. The oxygen partial pressure was monitored using an oxygen sensor installed downstream of the device. The oxygen partial pressure was controlled by mixing a small amount of the N₂/H₂ mixed gas with the nitrogen gas.

FIG. 27 shows a graph in which the measured electrical conductivity log [σ(Scm⁻¹)] is plotted on the vertical axis with respect to the oxygen partial pressure log [P(O₂)/atm] on the horizontal axis. It was strongly suggested that oxide ions were the dominant carriers in the electrical conduction of the compound of Test Example 1 because the total electrical conductivity was almost constant regardless of the oxygen partial pressure. Test Examples 2 to 21 having similar crystal structures are also considered to be compounds having oxide ions as dominant carriers.

Evaluation of Oxide Ion Transference Number

For Test Example 6, in order to determine the oxide ion transference number, the electromotive force was measured by an oxygen concentration cell using air gas and an N₂/O₂ mixed gas. After reducing the particle diameter of the sample prepared in the above-mentioned (Sample Synthesis) using a ball-mill, the sample was molded into pellets having a 25 mm φ by uniaxial pressing, and hydrostatic pressure was applied. The sample was sintered at 1200° C. for 12 hours to prepare a high-density sample of Test Example 6 for measuring electromotive force. The surface of the sample was scraped with a diamond slurry to make it smooth. The relative density of the pellets of Test Example 6 was 96.0%. A Pt paste having a diameter of about 10 mm was applied to the center of the pellet and heated at 1000° C. for 1 hour in order to remove the organic component contained in the platinum paste. The platinum paste and the platinum electrode were bonded with instant adhesives, and the alumina tube, glass seal, and sample were also bonded with instant adhesives and the platinum electrode was attached. A clamp made of alumina was used as a presser for the measurement. After heating at 1000° C. for 1 hour for adhesion of the glass seal, the oxide ion transference number of Test Example 6 was determined at 800° C. and 900° C. by measuring the electromotive force with an oxygen concentration cell.

FIG. 28 and FIG. 29 respectively show the electromotive force/mV plotted on the vertical axis and the oxygen partial pressure log [P(O₂)/atm] plotted on the horizontal axis for the result of electromotive force measurement of the oxygen concentration cell of Test Example 6 at temperatures of 800° C. and 900° C. The measured values showed that the electromotive force obtained was close to the theoretical value, in particular, the transference number of oxide ions at 900° C. was 94%, indicating that the oxide ions were the dominant carriers in the electrical conduction of the compound of Test Example 6, and that the compound of Test Example 6 was an oxide ion conductor. It is considered that the same transference numbers are shown for Test Examples 1 to 5 and 7 to 21 having similar crystal structures.

Structural Optimization by Density Functional Theory Calculation

Structural optimization calculations based on density functional theory were performed on Ba₇Nb₃MoMO₂₀. Here, M is a cation of at least one element selected from the group consisting of Ag, Al, At, Au, Be, Bi, Br, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, I, In, Ir, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, Np, Os, P, Pb, Pd, Po, Pr, Pt, Pu, Re, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Tc, Te, Ti, Tl, Tm, U, V, W, Xe, Y, Yb, Zn, and Zr. Structural optimization calculation was further performed on Ba₇Nb₃Mo₂O₂₀. Density functional theory calculation using generalized gradient approximation and PBE functional was performed using the program VASP. Tables 10 to 12 and 33 to 36 show the results of the lattice constants obtained by the structural optimization. The optimized structures of all compositions retain the crystal structure of the original hexagonal perovskite-related compounds, indicating the possibility that these compositions can be synthesized. These compositions are also considered to exhibit oxide ion conduction.

TABLE 10 Lattice constant Composition a(Å) b(Å) c(Å) α(°) β(°) γ(°) Ba₇Nb₃MoAgO₂₀ 5.939903 5.939903 16.7929 90 90 120 Ba₇Nb₃MoAlO₂₀ 5.900404 5.900404 16.743176 90 90 120 Ba₇Nb₃MoAtO₂₀ 6.010514 6.010514 16.860586 90 90 120 Ba₇Nb₃MoAuO₂₀ 5.94045 5.94045 16.776655 90 90 120 Ba₇Nb₃MoBeO₂₀ 5.904266 5.904266 17.167325 90 90 120 Ba₇Nb₃MoBiO₂₀ 5.992008 5.992008 16.836163 90 90 120 Ba₇Nb₃MoBrO₂₀ 5.944914 5.944914 16.810687 90 90 120 Ba₇Nb₃MoCdO₂₀ 6.00439 6.00439 16.915417 90 90 120 Ba₇Nb₃MoCoO₂₀ 5.881562 5.881562 16.737701 90 90 120 Ba₇Nb₃MoCrO₂₀ 5.883503 5.883503 16.738325 90 90 120 Ba₇Nb₃MoCuO₂₀ 5.906161 5.906161 16.761878 90 90 120 Ba₇Nb₃MoFeO₂₀ 5.883343 5.883343 16.73495 90 90 120 Ba₇Nb₃MoGaO₂₀ 5.933736 5.933736 16.764084 90 90 120 Ba₇Nb₃MoGeO₂₀ 5.902295 5.902295 16.768693 90 90 120 Ba₇Nb₃MoHfO₂₀ 5.968976 5.968976 16.790997 90 90 120 Ba₇Nb₃MoHgO₂₀ 5.987396 5.987396 16.86409 90 90 120 Ba₇Nb₃MoIO₂₀ 5.989267 5.989267 16.824409 90 90 120 Ba₇Nb₃MoInO₂₀ 5.993478 5.993478 16.823355 90 90 120

TABLE 11 Lattice constant Composition a(Å) b(Å) c(Å) α(°) β(°) γ(°) Ba₇Nb₃MoIrO₂₀ 5.921031 5.921031 16.776358 90 90 120 Ba₇Nb₃MoLiO₂₀ 5.973454 5.973454 16.848625 90 90 120 Ba₇Nb₃MoMgO₂₀ 5.962221 5.962221 16.770124 90 90 120 Ba₇Nb₃MoMnO₂₀ 5.885579 5.885579 16.746877 90 90 120 Ba₇Nb₃Mo₂O₂₀ 5.925905 5.925905 16.766074 90 90 120 Ba₇Nb₄MoO₂₀ 5.939187 5.939187 16.785091 90 90 120 Ba₇Nb₃MoNiO₂₀ 5.885521 5.885521 16.743637 90 90 120 Ba₇Nb₃MoNpO₂₀ 6.006428 6.006428 16.82175 90 90 120 Ba₇Nb₃MoOsO₂₀ 5.924442 5.924442 16.765013 90 90 120 Ba₇Nb₃MoPO₂₀ 5.84106 5.84106 16.713044 90 90 120 Ba₇Nb₃MoPbO₂₀ 6.006245 6.006245 16.85583 90 90 120 Ba₇Nb₃MoPdO₂₀ 5.923956 5.923956 16.778307 90 90 120 Ba₇Nb₃MoPoO₂₀ 6.006966 6.006966 16.867088 90 90 120 Ba₇Nb₃MoPtO₂₀ 5.92524 5.92524 16.779834 90 90 120 Ba₇Nb₃MoPuO₂₀ 6.004223 6.004223 16.827015 90 90 120 Ba₇Nb₃MoReO₂₀ 5.924747 5.924747 16.765651 90 90 120 Ba₇Nb₃MoRhO₂₀ 5.91523 5.91523 16.780144 90 90 120 Ba₇Nb₃MoRuO₂₀ 5.91787 5.91787 16.768206 90 90 120

TABLE 12 Lattice constant Composition a(Å) b(Å) c(Å) α(°) β(°) γ(°) Ba₇Nb₃MoSO₂₀ 5.993161 5.993161 17.062732 90 90 120 Ba₇Nb₃MoSbO₂₀ 5.945625 5.945625 16.788384 90 90 120 Ba₇Nb₃MoScO₂₀ 5.971676 5.971676 16.785252 90 90 120 Ba₇Nb₃MoSeO₂₀ 5.926511 5.926511 16.79729 90 90 120 Ba₇Nb₃MoSiO₂₀ 5.860383 5.860383 16.711353 90 90 120 Ba₇Nb₃MoSnO₂₀ 5.966884 5.966884 16.785986 90 90 120 Ba₇Nb₃MoTaO₂₀ 5.940375 5.940375 16.792127 90 90 120 Ba₇Nb₃MoTbO₂₀ 6.033514 6.033514 16.897624 90 90 120 Ba₇Nb₃MoTcO₂₀ 5.916867 5.916867 16.763218 90 90 120 Ba₇Nb₃MoTeO₂₀ 5.976477 5.976477 16.804157 90 90 120 Ba₇Nb₃MoTiO₂₀ 5.92103 5.92103 16.766404 90 90 120 Ba₇Nb₃MoTlO₂₀ 6.014835 6.014835 16.915364 90 90 120 Ba₇Nb₃MoUO₂₀ 6.007647 6.007647 16.826099 90 90 120 Ba₇Nb₃MoVO₂₀ 5.892306 5.892306 16.750264 90 90 120 Ba₇Nb₃MoWO₂₀ 5.92659 5.92659 16.751167 90 90 120 Ba₇Nb₃MoXeO₂₀ 6.074309 6.074309 16.752722 90 90 120 Ba₇Nb₃MoZnO₂₀ 5.955233 5.955233 16.784869 90 90 120 Ba₇Nb₃MoZrO₂₀ 5.978217 5.978217 16.793382 90 90 120

Test Examples 22 to 83

The compounds shown in the “Composition” of Test Examples 22 to 41 shown in Table 13, Test Examples 42 to 61 shown in Table 14, and Test Examples 62 to 83 shown in Table 15 were prepared according to the following procedure. In the composition shown in Tables 13 to 15, the oxygen amount calculated from the electrically neutral conditions is shown assuming that the oxidation number of Ba is +2, the oxidation number of Nb is +5, the oxidation number of Mo is +6, the oxidation number of oxygen O is −2, the oxidation number of W is +6, the oxidation number of V is +5, the oxidation number of Cr is +6, the oxidation number of Ge is +4, the oxidation number of Si is +4, the oxidation number of Zr is +4, the oxidation number of Ti is +4, the oxidation number of Al is +3, the oxidation number of Gd is +3, the oxidation number of Dy is +3, the oxidation number of Er is +3, the oxidation number of Ho is +3, the oxidation number of Tm is +3, the oxidation number of Yb is +3, and the oxidation number of Lu is +3, but the oxygen amount (20+z) is not limited to the values shown because the oxygen non-stoichiometry z depends on the cation molar ratio, temperature, oxygen partial pressure, synthesis method, and thermal history.

Test Examples 22 to 58 and 81 to 83

The compounds shown in “Composition” of Test Examples 22 to 41 in Table 13, Test Examples 42 to 58 in Table 14, and Test Examples 81 to 83 in Table 15 were prepared by the solid-phase reaction method. As starting materials, BaCO₃, Nb₂O₅, MoO₃, WO₃, V₂O₅, Cr₂O₃, MnO₂, GeO₂, SiO₂, and ZrO₂ were used. The starting materials were dried in advance in an electric furnace at 250 to 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for 30 minutes to 2 hours. The obtained mixture was calcined in the air at 900° C. for 10 to 12 hours using an electric furnace. The calcined mixture was repeatedly subjected to dry mixing and grinding and wet mixing and grinding using ethanol in an agate mortar for 30 minutes to 2 hours. The mixture was molded into cylindrical pellets having a diameter of 10 to 20 mm by pressurizing at 62 to 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1100° C. for 24 hours. As a result, pellets as a sintered body were obtained. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for about 20 minutes by a grinder made of tungsten carbide (WC) and then ground for 30 minutes to 1 hour by an agate mortar.

Test Examples 59 to 67

The compounds shown in “Composition” of Test Examples 59 to 61 in Table 14 and Test Examples 62 to 67 in Table 15 were prepared by the solid-phase reaction method. BaCO₃, WO₃, and V₂O₅ were used as starting materials. The starting materials were dried in advance in an electric furnace at 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for 1 hour. The obtained mixture was calcined in the air at 950° C. for 15 hours using an electric furnace. The calcined mixture was repeatedly subjected to mixing and grinding in an agate mortar for 1 hour in a dry manner and in a wet manner using ethanol. The mixture was molded into cylindrical pellets having a diameter of 10 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1020° C. for 24 hours. As a result, pellets as a sintered body were obtained. The electrical conductivity was measured using the obtained sintered body. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for about 20 minutes by a grinder made of tungsten carbide (WC) and then ground for about 1 hour by an agate mortar.

Test Examples 68 to 70

The compounds shown in “Composition” of Test Examples 68 to 70 in Table 15 were prepared by the solid-phase reaction method. BaCO₃, TiO₂, and MoO₃ were used as starting materials. The starting materials were dried in advance in an electric furnace at 250 to 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for 30 minutes. The obtained mixture was calcined in the air at 900° C. for 12 hours using an electric furnace. The calcined mixture was repeatedly subjected to mixing and grinding in an agate mortar for about 1 hour in a dry manner and in a wet manner using ethanol. The mixture was molded into cylindrical pellets having a diameter of 20 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1100° C. for 24 hours. The obtained sintered body was ground for 20 minutes by a grinder made of a tungsten carbide (WC), and then ground in an agate mortar for about 1 hour. The mixture was molded into cylindrical pellets having a diameter of 5 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1100° C. for 12 hours. As a result, pellets as a sintered body were obtained. The electrical conductivity was measured using the obtained sintered body. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for 20 minutes by a grinder made of tungsten carbide (WC) and then ground for about 1 hour by an agate mortar.

Test Example 71

The compound shown in “Composition” of Test Example 71 in Table 15 was prepared by the solid-phase reaction method. BaCO₃, MnO₂, and CaCO₃ were used as starting materials. The starting materials were dried in advance in an electric furnace at 250 to 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for about 1 hour. The obtained mixture was calcined in the air at 900° C. for 12 hours using an electric furnace. The calcined mixture was repeatedly subjected to dry mixing and grinding and wet mixing and grinding using ethanol in an agate mortar for 30 minutes. The mixture was molded into cylindrical pellets having a diameter of 20 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1200° C. for 12 hours. The obtained sintered body was ground for 20 minutes by a grinder made of a tungsten carbide (WC), and then ground in an agate mortar for about 1 hour. The mixture was molded into cylindrical pellets having a diameter of 5 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1400° C. for 24 hours. As a result, pellets as a sintered body were obtained. The electrical conductivity was measured using the obtained sintered body. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for 20 minutes by a grinder made of tungsten carbide (WC) and then ground for about 1 hour by an agate mortar.

Test Example 72

The compound shown in “Composition” of Test Example 72 in Table 15 was prepared by the solid-phase reaction method. BaCO₃, MnO₂, La₂O₃, and CaCO₃ were used as starting materials. The starting materials were dried in advance in an electric furnace at 250 to 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for about 1 hour. The obtained mixture was calcined in the air at 900° C. for 10 hours using an electric furnace. The calcined mixture was repeatedly subjected to mixing and grinding in an agate mortar for about 1 hour in a dry manner and in a wet manner using ethanol. The mixture was molded into cylindrical pellets having a diameter of 5 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1200° C. for 12 hours. The obtained sintered body was ground for 20 minutes by a grinder made of a tungsten carbide (WC), and then ground in an agate mortar for about 1 hour. The mixture was molded into cylindrical pellets having a diameter of 5 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1200° C. for 12 hours. As a result, pellets as a sintered body were obtained. The electrical conductivity was measured using the obtained sintered body. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for 20 minutes by a grinder made of tungsten carbide (WC) and then ground for about 1 hour by an agate mortar.

Test Example 73

The compound shown in “Composition” of Test Example 73 in Table 15 was prepared by the solid-phase reaction method. La₂CO₃, MnO₂, and CaCO₃ were used as starting materials. The starting materials were dried in advance in an electric furnace at 250 to 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for about 1 hour. The obtained mixture was calcined in the air at 900° C. for 12 hours using an electric furnace. The calcined mixture was repeatedly subjected to mixing and grinding in an agate mortar for about 1 hour in a dry manner and in a wet manner using ethanol. The mixture was molded into cylindrical pellets having a diameter of 5 mm by pressurizing at 150 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1200° C. for 12 hours. As a result, pellets as a sintered body were obtained. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for 20 minutes by a grinder made of tungsten carbide (WC) and then ground for about 1 hour by an agate mortar. This compound also has a crystal structure similar to that of the compounds of Test Examples 1 to 21, and thus is considered to have oxide ion conductance.

Test Examples 74 to 80

The compounds shown in the “composition” of Test Examples 74 to 80 in Table 15 were prepared by the solid-phase reaction method. BaCO₃, Al₂O₃, ZrO₂, Gd₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃ were used as starting materials. The starting materials were dried in advance in an electric furnace at 300° C. for 12 hours, and then weighed with an electronic balance so that the molar ratio of cations was at the desired chemical composition. Using an agate mortar, dry mixing and grinding and wet mixing and grinding using ethanol were repeatedly performed for 30 minutes. The obtained mixture was calcined in the air at 900° C. for 10 hours using an electric furnace. The calcined mixture was subjected to mixing and grinding in an agate mortar for 30 minutes in a dry manner. The mixture was molded into cylindrical pellets having a diameter of 20 mm by pressurizing at about 50 MPa using a uniaxial press. The obtained pellets were placed in an electric furnace and sintered in the air at 1600° C. for 12 hours to obtain a sintered body. The electrical conductivity was measured using the obtained sintered body. In order to evaluate the product phase of the obtained compound by X-ray diffraction (XRD), a part of the sintered body was ground for 20 minutes by a grinder made of tungsten carbide (WC) and then ground for about 30 minutes by an agate mortar.

Each table also shows the lattice constant and the lattice volume V of Test Examples 22 to 83. Further, for some Test Examples, the activation energy Ea (eV) of conductivity estimated from the temperature dependence of the total electrical conductivity is also shown. The transference number of Test Example 27 at 900° C. was 100%.

FIG. 30 shows a crystal structure of Ba₇Nb₄MoO₂₀ used in Test Example 22. In this figure, the space group is P-3m1 (No. 164), and the lattice constants are a=b=5.8602 Å and c=16.5311 Å. Test Examples 23 to 58 and 81 to 83, which are Ba₇Nb₄MoO₂₀-based materials, also have similar crystal structures. FIGS. 31 and 32 are a graph showing the XRD patterns of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)). FIG. 31 shows the measurement charts for x=0, 0.02, 0.04, 0.06, 0.08, 0.1, and FIG. 32 shows the measurement charts for x=0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.25, 0.3, 0.4, 0.5. The conductivity of Ba₇Nb_((4−x))Mo_((1+x))O_((20+z)) is plotted in a temperature-dependent manner for each value of x in FIG. 33 and in a composition-dependent manner for each temperature value in FIG. 34.

FIG. 35 is a graph showing the XRD pattern of Ba₇Nb_((4−y))MoCr_(y)O_((2+z)) used in Test Examples 40 to 44 and 46. The measurement charts for x=0.1, 0.2, 0.25, 0.3, 0.4, 0.5 are shown. The conductivity of Ba7Nb(4−x)Mo(1+x)O(20+z) is plotted in a temperature-dependent manner in FIG. 36.

The conductivity of Ba₇Nb_((4−y))MoCr_(y)O_((20+z)) used in Test Examples 22, 40 to 44, and 46 is plotted in a composition-dependent manner in FIG. 37.

FIG. 38 is a graph showing the XRD patterns of Ba₇Nb_((4−y))MoW_(y)O_((20+z)) used in Test Examples 52 to 58 and 81 and 83. FIG. 39 shows the total electrical conductivity of Ba₇Nb_((4−y))MoW_(y)O_((20+z)) in a temperature-dependent manner. FIG. 40 shows the total electrical conductivity of Ba₇Nb_((4−y))MoW_(y)O_((20+z)) in a composition-dependent manner.

FIG. 41 is a graph showing XRD patterns of Ba₇Nb_(3.9)MoM_(0.1)O_((20+z)) (M is V, Mn, Ge, Si, or Zr), Ba₇Nb₄Mo_(0.9)M_(0.1)O_((20+z)) (M is V or Mn), and Ba₇Nb_(4.05)Mo_(0.95)O_((20+z)) as other solid solutions used in Test Examples 38, 39, 45, and 47 to 51. FIG. 42 shows the electrical conductivity of the solid solutions used in Test Examples 38, 39, and 47 to 50 in a temperature-dependent manner.

FIG. 43 shows the crystal structure of a Ba₃WVO₈₅-based material used in Test Examples 59 to 67. At present, the Ba₃WVO_(8.5) system is said to have the crystal structure of FIG. 43(a), but the crystal structures of FIGS. 43(b) and (c) are proposed from the analysis results. In these figures, the space group is R-3m (No. 166), and the lattice constants are a=b=5.808130 (19) Å and c=21.094919 (21) Å. FIG. 44 is a graph showing the XRD patterns of Ba₃W_((1−x))V_((1+x))O_((8.5+z)). FIG. 45 shows the electrical conductivity in a temperature-dependent manner. FIG. 46 shows the electrical conductivity in a composition-dependent manner. The electrical conductivity increases as the temperature rises. At 600° C., the electrical conductivity a of Ba₃W_(1.6)V_(0.4)O_(8.8) of Test Example 66 was 85 times higher than the electrical conductivity of Ba₃WVO_(8.5) of Test Example 59, indicating that the electrical conductivity was improved by increasing the W amount. The same applies to Test Examples 59 to 65 and 67, which are also Ba₃WVO_(8.5)-based materials.

FIG. 47 shows the P (O₂) dependence of conductivity for Ba₃W_(1.6)V_(0.4)O_(8.8) of Test Example 66. It is suggested that oxide ions are the dominant carriers in the region in the electrical conduction of the compound of Test Example 66 because there is a region where the total electrical conductivity is almost constant regardless of the oxygen partial pressure. FIG. 48 shows the conductivity of Ba₃W_(1.6)V_(0.4)O_(8.8) in dry air and in moist air. No change in total electrical conductivity was observed in measurements in moist air and dry air with respect to Test Example 66, strongly suggesting that no proton conduction occurred in Test Example 66. The same applies to Test Examples 59 to 65 and 67, which are also Ba₃WVO_(8.5)-based materials.

FIG. 49 shows the crystal structure of a Ba₃MoTiO₈-based material used in Test Examples 68 to 70. In this figure, the space group is R-3m (No. 166), and the lattice constants are a=b=5.9548 Å and c=21.2924 Å. FIG. 50 is a graph showing the XRD pattern of Ba₃Mo_((1−x))Ti_((1+x))O_((8+z)).

FIG. 51 shows the temperature dependence of the electrical conductivity of Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) and Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) in which the excess amount x of Ti is −0.1 and −0.2. The temperature dependence of the electrical conductivity of Ba₃MoTiO₈ in which the excess amount x of Mo of Test Example of the present example is 0.0 is also shown. All of the samples in which the excess amount x of Mo is in the range of −0.1 and −0.2 show higher electrical conductivity than the sample of Ba₃MoTIO₈ (Test Example 68) in which the excess amount x of Mo is 0.0. At 620° C. or less, the sample in which the excess amount x of Mo is −0.1 has the highest electrical conductivity, and high electrical conductivity is maintained even at a low temperature of about 300° C.

Oxygen Partial Pressure Dependence of Total Electrical Conductivity

For Test Example 69, the oxygen partial pressure dependence of total electrical conductivity was measured. FIG. 52 shows a graph in which the measured electrical conductivity log [σ(Scm⁻¹)] is plotted on the vertical axis with respect to the oxygen partial pressure log [P(O₂)/atm] on the horizontal axis. It was strongly suggested that oxide ions were the dominant carriers in the electrical conduction of the compound of Test Example 69 because the total electrical conductivity was almost constant regardless of the oxygen partial pressure. The same applies to Test Examples 68 and 70, which are also Ba₃MoTiO₈-based materials.

FIG. 53 shows the crystal structure of a Ba₇Ca₂Mn₅O₂₀-based material used in Test Example 71. In this figure, the space group R-3m (No. 166), the lattice constants a=b=5.8195 Å, and c=51.3701 Å. FIG. 54 is a graph showing the XRD pattern of Ba₇Ca₂Mn₅O₂₀. FIG. 55 shows the total electrical conductivity of Ba₇Ca₂Mn₅O₂₀ in a temperature-dependent manner.

FIG. 56 shows the crystal structure of a Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉-based material used in Test Example 72. The space group of Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ is C2/m (No. 12), and the lattice constants are a=9.8394 Å, b=5.6823 Å, c=15.6435 Å, and β=102.09°. FIG. 57 is a graph showing the XRD pattern of Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉. FIG. 58 shows the total electrical conductivity of Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ in a temperature-dependent manner.

FIG. 59 shows the crystal structure of a La₂Ca₂MnO₇-based material used in Test Example 73. In this figure, the space group is R-3m (No. 166), and the lattice constants are a=b=5.6200 Å and c=17.2954 Å. FIG. 60 is a graph showing the XRD pattern of La₂Ca₂MnO₇.

FIG. 61 shows the crystal structure of the Ba₅M₂Al₂ZrO₁₃-based material used in Test Examples 74 to 80. In this figure, the space group is P63/mmc (No. 194), and the lattice constants are a=b=5.9629 Å and c=24.7340 Å. FIG. 62 is a graph showing the XRD patterns of Ba₅M₂Al₂ZrO₁₃ (M is Gd, Dy, Er, Ho, Tm, Yb, Lu). FIG. 63 shows the total electrical conductivity of Ba₅M₂Al₂ZrO₁₃ measured in the air in a temperature-dependent manner. For Test Example 76, the total electrical conductivity in dry air was also shown in a temperature-dependent manner. The reduced conductivity in dry air suggests that Test Example 76 exhibits proton conduction. The same applies to Test Examples 74, 75, and 77 to 80, which are also Ba₅M₂Al₂ZrO₁₃-based materials.

TABLE 13 Activation Lattice constant energy Composition a[Å] b[Å] c[Å] α[°] β[°] γ[°] V[Å³] E_(a)(eV) Example 22 Ba₇Nb₄MoO₂₀ 5.8602 5.8602 16.5311 90 90 120 491.72 0.52 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 5.8606 5.8606 16.5361 90 90 120 491.87 0.49 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 5.8605 5.8605 16.5406 90 90 120 491.99 0.49 Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 5.8622 5.8622 16.5337 90 90 120 492.06 0.47 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 5.8598 5.8598 16.5288 90 90 120 491.50 0.51 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 5.8585 5.8585 16.5408 90 90 120 491.65 0.44 Example 28 Ba₇Nb_(3.88)Mo_(1.12)O_(20.06) 5.8601 5.8601 16.5315 90 90 120 491.65 0.48 Example 29 Ba₇Nb_(3.86)Mo_(1.14)O_(20.07) 5.8608 5.8608 16.5339 90 90 120 491.83 0.54 Example 30 Ba₇Nb_(3.84)Mo_(1.16)O_(20.08) 5.8605 5.8605 16.5337 90 90 120 491.78 0.52 Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 5.8604 5.8604 16.5347 90 90 120 491.79 0.47 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 5.8611 5.8611 16.5362 90 90 120 491.95 0.41 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 5.8594 5.8594 16.5364 90 90 120 491.67 0.42 Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 5.8631 5.8631 16.5417 90 90 120 492.45 0.43 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 5.8721 5.8721 16.519 90 90 120 493.29 0.44 Example 36 Ba₇Nb_(3.6)Mo_(1.4)O_(20.2) 5.865 5.8650 16.544 90 90 120 492.84 Example 37 Ba₇Nb_(3.5)Mo_(1.5)O_(20.25) 5.8759 5.8759 16.5215 90 90 120 494.00 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 5.8584 5.8584 16.5259 90 90 120 491.19 0.53 Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 5.8557 5.8557 16.5114 90 90 120 490.32 0.69 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 5.8539 5.8539 16.5122 90 90 120 490.04 0.59 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 5.8474 5.8474 16.4985 90 90 120 488.54 0.43

TABLE 14 Activation Lattice constant energy Composition a[Å] b[Å] c[Å] a[Å] b[Å] γ[°] a[Å] b[Å] Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 5.8546 5.8546 16.5319 90 90 120 490.74 0.58 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 5.8474 5.8474 16.5084 90 90 120 488.84 0.47 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 5.8491 5.8491 16.5353 90 90 120 489.92 0.48 Example 45 Ba₇Nb₄Mo_(0.9)Mn_(0.1)O_(20.05) 5.8550 5.8550 16.5218 90 90 120 490.50 Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 5.8483 5.8483 16.5368 90 90 120 489.83 0.44 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 5.8555 5.8555 16.5156 90 90 120 490.41 0.59 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 5.8579 5.8579 16.5257 90 90 120 491.10 0.38 Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 5.8597 5.8597 16.5204 90 90 120 491.26 0.69 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 5.8557 5.8557 16.5206 90 90 120 490.59 0.52 Example 51 Ba₇Nb_(3.9)MoMn_(0.1)O_(19.95) 5.8609 5.8609 16.5533 90 90 120 492.4292484 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 5.877557 5.877557 16.5703 90 90 120 495.741 0.48 Example 53 Ba₇Nb_(3.8)MoW_(0.2)O_(20.1) 5.86035 5.86035 16.5186 90 90 120 491.31 0.51 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 5.856966 5.856966 16.522297 90 90 120 490.87 0.59 Example 55 Ba₇Nb_(3.6)MoW_(0.4)O_(20.2) 5.86134 5.86134 16.53054 90 90 120 491.83 0.59 Example 56 Ba₇Nb_(3.5)MoW_(0.5)O_(20.25) 5.857308 5.857308 16.51766 90 90 120 490.77 0.54 Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 5.857222 5.857222 16.5199 90 90 120 490.82 0.60 Example 58 Ba₇Nb_(3.2)MoW_(0.8)O_(20.4) 5.853921 5.853921 16.52247 90 90 120 490.34 0.66 Example 59 Ba₃WVO_(8.5) 5.808130(19) 5.808130(19) 21.094919(21) 90 90 120 615.4(9) 1.72 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 5.822 5.822 21.159 90 90 120 621.19 1.67 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 5.822 5.822 21.149 90 90 120 620.80 1.81

TABLE 15 Activation Lattice constant energy Composition a[Å] b[Å] c[Å] a[Å] b[Å] γ[°] a[Å] b[Å] Test Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 5.823 5.823 21.132 90 90 120 620.61 1.73 Test Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 5.824 5.824 21.119 90 90 120 620.31 1.67 Test Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 5.816 5.816 21.021 90 90 120 615.81 1.40 Test Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 5.821 5.821 21.054 90 90 120 617.88 1.11 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 5.821531(7) 5.821531(7) 21.03203(9) 90 90 120 617.290(4) 1.02 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 5.8185566 5.8185566 20.9976252 90 90 120 615.65 1.17 Test Example 68 Ba₃MoTiO₈ 5.9548 5.9548 21.2924 90 90 120 653.89 1.00 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 5.9484 5.9484 21.2626 90 90 120 651.56 0.78 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 5.9343 5.9343 21.2216 90 90 120 647.21 1.03 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 5.8195 5.8195 51.3701 90 90 120 1506.66 0.85 Test Example 72 Ba_(2.6)Ca_(2.4)La₄Mn₄O₁₉ 9.8394 5.6823 15.6435 90 102.093 90 855.23 Test Example 73 La₂Ca₂MnO₇ 5.6200 5.6200 17.2954 90 90 120 473.09 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 5.9807 5.9807 24.661 90 90 120 776.68 1.28 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 5.947 5.947 24.817 90 90 120 774.07 0.19 Test Example 76 Ba₅Er₂Al₂ZrO₁₃ 5.9547 5.9462 24.709 90 90 120 761.62 0.25 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 5.9462 5.9348 24.672 90 90 120 763.68 0.26 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 5.9348 5.9269 24.635 90 90 120 759.31 0.52 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 5.9269 5.9262 24.603 90 90 120 754.39 0.27 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 5.9262 5.9269 24.611 90 90 120 753.88 0.24 Test Example 81 Ba₇Nb₃MoWO_(20.5) 5.853355 5.853355 16.5167 90 90 120 490.08 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.075) 5.860241 5.860241 16.5322 90 90 120 491.69 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.125) 5.857922 5.857922 16.51918 90 90 120 490.92

Tables 16 to 32 show the results of Test Examples in which electrical conductivity was measured among Test Examples 22 to 83. In the composition shown in Tables 16 to 32, the oxygen amount calculated from the electrically neutral conditions is shown assuming that the oxidation number of Ba is +2, the oxidation number of Nb is +5, the oxidation number of Mo is +6, the oxidation number of oxygen O is −2, the oxidation number of W is +6, the oxidation number of V is +5, the oxidation number of Cr is +6, the oxidation number of Ge is +4, the oxidation number of Si is +4, the oxidation number of Zr is +4, the oxidation number of Ti is +4, the oxidation number of Al is +3, the oxidation number of Gd is +3, the oxidation number of Dy is +3, the oxidation number of Er is +3, the oxidation number of Ho is +3, the oxidation number of Tm is +3, the oxidation number of Yb is +3, and the oxidation number of Lu is +3, but the oxygen amount (20+z) is not limited to the values shown because the oxygen non-stoichiometry z depends on the cation molar ratio, temperature, oxygen partial pressure, synthesis method, and thermal history.

TABLE 16 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 22 Ba₇Nb₄MoO₂₀ 306° C. −4.6 Example 22 Ba₇Nb₄MoO₂₀ 406° C. −3.9 Example 22 Ba₇Nb₄MoO₂₀ 506° C. −3.4 Example 22 Ba₇Nb₄MoO₂₀ 606° C. −3.0 Example 22 Ba₇Nb₄MoO₂₀ 706° C. −2.7 Example 22 Ba₇Nb₄MoO₂₀ 807° C. −2.5 Example 22 Ba₇Nb₄MoO₂₀ 907° C. −2.3 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 306° C. −4.5 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 406° C. −3.8 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 506° C. −3.3 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 606° C. −2.9 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 706° C. −2.7 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 806° C. −2.5 Example 23 Ba₇Nb_(3.98)Mo_(1.02)O_(20.01) 906° C. −2.3 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 307° C. −4.7 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 410° C. −3.6 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 510° C. −2.9 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 610° C. −2.6 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 710° C. −2.5 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 809° C. −2.4 Example 24 Ba₇Nb_(3.96)Mo_(1.04)O_(20.02) 909° C. −2.3

TABLE 17 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 304° C. −4.3 Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 406° C. −3.6 Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 506° C. −3.1 Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 606° C. −2.8 Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 706° C. −2.6 Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 806° C. −2.4 Example 25 Ba₇Nb_(3.94)Mo_(1.06)O_(20.03) 906° C. −2.2 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 306° C. −4.4 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 408° C. −3.7 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 510° C −3.1 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 609° C. −2.8 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 709° C. −2.5 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 809° C. −2.3 Example 26 Ba₇Nb_(3.92)Mo_(1.08)O_(20.04) 908° C. −2.1 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 305° C. −4.1 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 407° C. −3.4 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 505° C. −2.9 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 606° C. −2.6 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 706° C. −2.4 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 807° C. −2.2 Example 27 Ba₇Nb_(3.9)Mo_(1.1)O_(20.05) 906° C. −2.1

TABLE 18 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 28 Ba7Nb_(3.88)Mo_(1.12)O_(20.06) 307° C. −4.3 Example 28 Ba7Nb_(3.88)Mo_(1.12)O_(20.06) 406° C. −3.6 Example 28 Ba7Nb_(3.88)Mo_(1.12)O_(20.06) 507° C. −3.1 Example 28 Ba7Nb_(3.88)Mo_(1.12)O_(20.06) 607° C. −2.7 Example 28 Ba7Nb_(3.88)Mo_(1.12)O_(20.06) 707° C. −2.5 Example 28 Ba7Nb_(3.88)Mo_(1.12)O_(20.06) 807° C. −2.3 Example 28 Ba7Nb_(3.88)Mo_(1.12)O_(20.06) 906° C. −2.2 Example 29 Ba7Nb_(3.86)Mo_(1.14)O_(20.07) 306° C. −4.2 Example 29 Ba7Nb_(3.86)Mo_(1.14)O_(20.07) 407° C. −3.3 Example 29 Ba7Nb_(3.86)Mo_(1.14)O_(20.07) 506° C. −2.8 Example 29 Ba7Nb_(3.86)Mo_(1.14)O_(20.07) 606° C. −2.3 Example 29 Ba7Nb_(3.86)Mo_(1.14)O_(20.07) 706° C. −2.1 Example 29 Ba7Nb_(3.86)Mo_(1.14)O_(20.07) 806° C. −1.9 Example 29 Ba7Nb_(3.86)Mo_(1.14)O_(20.07) 907° C. −1.8 Example 30 Ba7Nb_(3.84)Mo_(1.16)O_(20.08) 305° C. −4.0 Example 30 Ba7Nb_(3.84)Mo_(1.16)O_(20.08) 406° C. −3.3 Example 30 Ba7Nb_(3.84)Mo_(1.16)O_(20.08) 506° C. −2.7 Example 30 Ba7Nb_(3.84)Mo_(1.16)O_(20.08) 606° C. −2.3 Example 30 Ba7Nb_(3.84)Mo_(1.16)O_(20.08) 706° C. −2.1 Example 30 Ba7Nb_(3.84)Mo_(1.16)O_(20.08) 806° C. −1.9 Example 30 Ba7Nb_(3.84)Mo_(1.16)O_(20.08) 906° C. −1.8

TABLE 19 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 307° C. −3.7 Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 408° C. −3.0 Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 509° C. −2.5 Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 610° C. −2.1 Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 709° C. −2.0 Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 809° C. −1.8 Example 31 Ba₇Nb_(3.82)Mo_(1.18)O_(20.09) 908° C. −1.7 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 306° C. −3.4 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 406° C. −2.8 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 506° C. −2.3 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 606° C. −2.0 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 706° C. −1.8 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 807° C. −1.7 Example 32 Ba₇Nb_(3.8)Mo_(1.2)O_(20.1) 906° C. −1.6 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 304° C. −3.8 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 406° C. −3.1 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 505° C. −2.7 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 606° C. −2.4 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 706° C. −2.2 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 807° C. −2.0 Example 33 Ba₇Nb_(3.78)Mo_(1.22)O_(20.11) 907° C. −1.9

TABLE 20 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 305° C. −3.8 Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 407° C. −3.1 Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 507° C. −2.7 Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 607° C. −2.4 Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 706° C. −2.2 Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 807° C. −2.0 Example 34 Ba₇Nb_(3.75)Mo_(1.25)O_(20.125) 907° C. −1.9 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 305° C. −3.8 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 406° C. −3.1 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 506° C. −2.7 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 607° C. −2.4 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 706° C. −2.2 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 807° C. −2.0 Example 35 Ba₇Nb_(3.7)Mo_(1.3)O_(20.15) 907° C. −1.9 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 306° C. −5.4 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 409° C. −4.2 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 508° C. −3.5 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 608° C. −3.2 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 707° C. −3.2 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 806° C. −3.1 Example 38 Ba₇Nb₄Mo_(0.9)V_(0.1)O_(19.95) 908° C. −2.9

TABLE 21 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 304° C. −5.8 Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 405° C. −4.8 Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 506° C. −4.2 Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 607° C. −3.6 Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 707° C. −3.1 Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 807° C. −2.9 Example 39 Ba₇Nb_(3.9)MoV_(0.1)O₂₀ 908° C. −2.8 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 306° C. −4.5 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 406° C. −3.6 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 507° C. −3.0 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 607° C. −2.6 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 707° C. −2.2 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 807° C. −2.1 Example 40 Ba₇Nb_(3.9)MoCr_(0.1)O_(20.05) 907° C. −2.0 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 303° C. −3.9 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 403° C. −3.2 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 504° C. −2.7 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 605° C. −2.4 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 705° C. −2.2 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 806° C. −2.1 Example 41 Ba₇Nb_(3.8)MoCr_(0.2)O_(20.1) 906° C. −2.0

TABLE 22 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 307° C. −4.6 Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 407° C. −3.8 Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 507° C. −3.2 Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 607° C. −2.7 Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 707° C. −2.4 Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 807° C. −2.2 Example 42 Ba₇Nb_(3.75)MoCr_(0.25)O_(20.125) 907° C. −2.1 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 307° C. −4.0 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 407° C. −3.2 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 507° C. −2.7 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 607° C. −2.4 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 707° C. −2.1 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 807° C. −2.0 Example 43 Ba₇Nb_(3.7)MoCr_(0.3)O_(20.15) 906° C. −2.0 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 307° C. −4.2 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 407° C. −3.4 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 507° C. −2.9 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 607° C. −2.5 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 707° C. −2.2 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 807° C. −2.1 Example 44 Ba₇Nb_(3.6)MoCr_(0.4)O_(20.2) 907° C. −2.2

TABLE 23 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 305° C. −4.2 Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 406° C. −3.5 Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 506° C. −3.0 Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 606° C. −2.6 Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 706° C. −2.3 Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 806° C. −2.3 Example 46 Ba₇Nb_(3.5)MoCr_(0.5)O_(20.25) 907° C. −2.3 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 303° C. −5.6 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 406° C. −4.7 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 506° C. −4.0 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 607° C. −3.5 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 707° C. −3.3 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 808° C. −3.1 Example 47 Ba₇Nb_(3.9)MoGe_(0.1)O_(19.95) 908° C. −2.9 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 309° C. −5.2 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 409° C. −4.1 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 510° C. −4.1 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 610° C. −4.0 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 709° C. −3.6 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 809° C. −3.5 Example 48 Ba₇Nb_(3.9)MoSi_(0.1)O_(19.95) 908° C. −3.3

TABLE 24 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 305° C. −6.2 Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 404° C. −5.5 Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 504° C. −4.6 Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 606° C. −4.0 Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 707° C. −3.6 Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 807° C. −3.4 Example 49 Ba₇Nb_(3.9)MoZr_(0.1)O_(19.95) 907° C. −3.3 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 305° C. −4.8 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 406° C. −3.7 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 506° C. −3.0 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 607° C. −2.7 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 707° C. −2.6 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 807° C. −2.5 Example 50 Ba₇Nb_(4.05)Mo_(0.95)O_(19.975) 907° C. −2.4 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 306° C. −4.1 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 409° C. −3.3 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 508° C. −2.8 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 608° C. −2.5 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 707° C. −2.2 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 808° C. −2.0 Example 52 Ba₇Nb_(3.9)MoW_(0.1)O_(20.05) 907° C. −1.9

TABLE 25 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 53 Ba₇Nb_(3.8)MoW_(0.2)O_(20.1) 506° C. −2.8 Example 53 Ba₇Nb_(3.8)MoW_(0.2)O_(20.1) 606° C. −2.3 Example 53 Ba₇Nb_(3.8)MoW_(0.2)O_(20.1) 706° C. −2.0 Example 53 Ba₇Nb_(3.8)MoW_(0.2)O_(20.1) 806° C. −1.8 Example 53 Ba₇Nb_(3.8)MoW_(0.2)O_(20.1) 906° C. −1.6 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 306° C. −4.4 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 407° C. −3.5 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 506° C. −2.9 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 606° C. −2.5 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 706° C. −2.1 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 806° C. −1.9 Example 54 Ba₇Nb_(3.7)MoW_(0.3)O_(20.15) 906° C. −1.7 Example 56 Ba₇Nb_(3.5)MoW_(0.5)O_(20.25) 506° C. −2.9 Example 56 Ba₇Nb_(3.5)MoW_(0.5)O_(20.25) 606° C. −2.4 Example 56 Ba₇Nb_(3.5)MoW_(0.5)O_(20.25) 706° C. −2.1 Example 56 Ba₇Nb_(3.5)MoW_(0.5)O_(20.25) 806° C. −1.8 Example 56 Ba₇Nb_(3.5)MoW_(0.5)O_(20.25) 906° C. −1.6

TABLE 26 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 306° C. −4.8 Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 407° C. −3.6 Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 506° C. −3.0 Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 606° C. −2.5 Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 706° C. −2.1 Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 806° C. −1.9 Example 57 Ba₇Nb_(3.4)MoW_(0.6)O_(20.3) 906° C. −1.7 Example 58 Ba₇Nb_(3.2)MoW_(0.8)O_(20.4) 506° C. −2.9 Example 58 Ba₇Nb_(3.2)MoW_(0.8)O_(20.4) 606° C. −2.4 Example 58 Ba₇Nb_(3.2)MoW_(0.8)O_(20.4) 706° C. −2.0 Example 58 Ba₇Nb_(3.2)MoW_(0.8)O_(20.4) 806° C. −1.7 Example 58 Ba₇Nb_(3.2)MoW_(0.8)O_(20.4) 906° C. −1.5 Example 59 Ba₃WVO_(8.5) 602.8° C. −5.5 Example 59 Ba₃WVO_(8.5) 653° C. −5.1 Example 59 Ba₃WVO_(8.5) 703.2° C. −4.6 Example 59 Ba₃WVO_(8.5) 753.6° C. −4.2 Example 59 Ba₃WVO_(8.5) 803.9° C. −3.9 Example 59 Ba₃WVO_(8.5) 854.2° C. −3.5 Example 59 Ba₃WVO_(8.5) 904.2° C. −3.2 Example 59 Ba₃WVO_(8.5) 954.5° C. −2.9 Example 59 Ba₃WVO_(8.5) 1004.6° C. −2.6

TABLE 27 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 602.3° C. −6.1 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 652.4° C. −5.3 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 702.8° C. −5.1 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 753.1° C. −4.7 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 803.4° C. −4.3 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 853.5° C. −4.7 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 903.9° C. −5.1 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 953.8° C. −5.3 Example 60 Ba₃W_(0.9)V_(1.1)O_(8.45) 1004° C. −6.1 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 602.8° C. −5.6 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 653° C. −5.2 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 703.2° C. −4.8 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 753.6° C. −4.5 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 803.9° C. −4.1 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 854.2° C. −3.8 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 904.2° C. −3.5 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 954.5° C. −3.2 Example 61 Ba₃W_(0.95)V_(1.05)O_(8.475) 1004.6° C. −2.9 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 603° C. −5.3 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 653.1° C. −5.0 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 703.4° C. −4.7 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 754° C. −4.4 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 804.3° C. −4.0 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 854.6° C. −3.7 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 904.7° C. −3.3 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 954.9° C. −3.0 Example 62 Ba₃W_(1.05)V_(0.95)O_(8.525) 1004.9° C. −2.7

TABLE 28 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 602.7° C. −5.2 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 653.1° C. −4.9 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 703.6° C. −4.6 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 754° C. −4.2 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 804.1° C. −3.9 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 854.5° C. −3.5 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 904.7° C. −3.2 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 955.1° C. −2.9 Example 63 Ba₃W_(1.1)V_(0.9)O_(8.55) 1005.2° C. −2.6 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 602.8° C. −4.9 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 653° C. −4.5 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 703.3° C. −4.1 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 753.9° C. −3.8 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 804.4° C. −3.5 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 854.6° C. −3.2 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 902.8° C. −2.9 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 952.5° C. −2.7 Example 64 Ba₃W_(1.25)V_(0.75)O_(8.625) 1004.3° C. −2.4 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 602.9° C. −4.1 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 653.1° C. −3.8 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 703.4° C. −3.5 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 753.9° C. −3.2 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 804.2° C. −2.9 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 854.4° C. −2.7 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 904.8° C. −2.5 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 955° C. −2.3 Example 65 Ba₃W_(1.5)V_(0.5)O_(8.75) 1005° C. −2.1

TABLE 29 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 602.6° C. −3.5 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 653° C. −3.2 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 703.3° C. −2.9 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 753.7° C. −2.7 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 804° C. −2.4 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 854.1° C. −2.2 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 904.5° C. −2.0 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 954.9° C. −1.9 Test Example 66 Ba₃W_(1.6)V_(0.4)O_(8.8) 1004° C. −1.7 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 602.55° C. −4.7 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 652.35° C. −4.4 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 702.85° C. −4.1 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 753.15° C. −3.9 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 803.65° C. −3.6 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 854.05° C. −3.4 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 904.25° C. −3.2 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 954.35° C. −2.9 Test Example 67 Ba₃W_(1.75)V_(0.25)O_(8.875) 1004.65° C. −2.8 Test Example 68 Ba₃MoTiO₈ 902.7° C. −2.9 Test Example 68 Ba₃MoTiO₈ 854.4° C. −3.0 Test Example 68 Ba₃MoTiO₈ 803.6° C. −3.1 Test Example 68 Ba₃MoTiO₈ 753.2° C. −3.4 Test Example 68 Ba₃MoTiO₈ 702.1° C. −3.7 Test Example 68 Ba₃MoTiO₈ 651.4° C. −4.0 Test Example 68 Ba₃MoTiO₈ 600.9° C. −4.3 Test Example 68 Ba₃MoTiO₈ 549.9° C. −4.7 Test Example 68 Ba₃MoTiO₈ 495.2° C. −5.0 Test Example 68 Ba₃MoTiO₈ 450.2° C. −5.5

TABLE 30 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 904.2° C. −2.2 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 853.6° C. −2.2 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 802.9° C. −2.3 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 752.6° C. −2.5 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 701.7° C. −2.6 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 651.5° C. −2.8 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 601° C. −3.0 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 550.4° C. −3.3 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 449.5° C. −3.8 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 395.5° C. −4.3 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 347.5° C. −4.7 Test Example 69 Ba₃Mo_(1.1)Ti_(0.9)O_(8.1) 295.8° C. −5.2 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 804.7° C. −2.2 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 753.3° C. −2.4 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 703.1° C. −2.5 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 653° C. −2.8 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 602.3° C. −3.1 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 552.5° C. −3.4 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 501.8° C. −3.7 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 456.8° C. −4.2 Test Example 70 Ba₃Mo_(1.2)Ti_(0.8)O_(8.2) 419° C. −4.5 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 300.7° C. −4.5 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 401.2° C. −3.7 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 506.3° C. −3.0 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 603.6° C. −2.4 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 704.2° C. −1.9 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 804.9° C. −1.4 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 905.5° C. −1.1 Test Example 71 Ba₇Ca₂Mn₅O₂₀ 1005.6° C. −0.8 Test Example 72 Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ 676° C. −2 Test Example 72 Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ 775° C. −1.8 Test Example 72 Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ 826° C. −1.7 Test Example 72 Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ 876° C. −1.6 Test Example 72 Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ 926° C. −1.5 Test Example 72 Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ 976° C. −1.4 Test Example 72 Ba_(2.6)Ca_(1.4)La₄Mn₄O₁₉ 1027° C. −1.4

TABLE 31 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 292.4° C. −6.3 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 345.1° C. −5.9 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 396.8° C. −5.6 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 447.9° C. −5.4 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 498.4° C. −5.2 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 599.7° C. −5.0 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 700.5° C. −4.8 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 801.6° C. −4.5 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 904.8° C. −4.1 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 1001.1° C. −3.7 Test Example 74 Ba₅Gd₂Al₂ZrO₁₃ 1170.3° C. −3.0 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 299.9° C. −3.4 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 350.5° C. −3.2 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 401.3° C. −3.1 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 452.1° C. −3.1 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 504.3° C. −3.1 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 604.9° C. −3.2 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 704.9° C. −3.2 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 804.9° C. −3.2 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 905.2° C. −3.2 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 1005.6° C. −3.1 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 1105.5° C. −3.0 Test Example 75 Ba₅Dy₂Al₂ZrO₁₃ 1204.9° C. −2.8 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 299.2° C. −3.5 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 352.4° C. −3.1 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 403.9° C. −2.8 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 453.9° C. −2.8 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 503.8° C. −2.8 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 505.8° C. −2.8 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 554.2° C. −2.9 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 604.5° C. −3.0 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 705° C. −3.0 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 805.3° C. −3.0 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 905.6° C. −2.9 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 1005.5° C. −2.8 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 1105.3° C. −2.7 Test Example 76 (in air) Ba₅Er₂Al₂ZrO₁₃ 1204.8° C. −2.6 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 317.8° C. −4.6 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 404.7° C. −4.2 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 508.2° C. −4.1 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 600° C. −4.0 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 702.9° C. −3.9 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 805.7° C. −3.8 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 1007.4° C. −3.5 Test Example 76 (in dry air) Ba₅Er₂Al₂ZrO₁₃ 1150.1° C. −3.2 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 299.9° C. −2.9 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 351.6° C. −2.8 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 399.2° C. −2.7 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 449.3° C. −2.7 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 499.6° C. −2.7 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 601.2° C. −2.8 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 701.8° C. −2.9 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 802.5° C. −2.8 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 903.2° C. −2.7 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 1003.7° C. −2.6 Test Example 77 Ba₅Ho₂Al₂ZrO₁₃ 1203.9° C. −2.4

TABLE 32 Total electrical conductivity (~oxide ion conductivity) and measured temperature Composition Temperature log (σ_(total)(S cm⁻¹)) Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 299° C. −3.5 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 348.4° C. −3.3 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 398.4° C. −3.2 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 448.7° C. −3.3 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 499.2° C. −3.4 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 602.4° C. −3.4 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 701.3° C. −3.3 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 801.9° C. −3.1 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 903.1° C. −2.9 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 1039.8° C. −2.6 Test Example 78 Ba₅Tm₂Al₂ZrO₁₃ 1206.5° C. −2.4 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 304.1° C. −3.3 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 404.3° C. −2.9 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 503.7° C. −2.8 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 604.2° C. −2.8 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 704.9° C. −2.9 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 804.5° C. −2.8 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 904.9° C. −2.7 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 1005.6° C. −2.6 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 1105.1° C. −2.5 Test Example 79 Ba₅Yb₂Al₂ZrO₁₃ 1204.6° C. −2.4 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 305.7° C. −5.0 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 354.3° C. −4.5 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 403.4° C. −4.1 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 452.9° C. −3.9 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 502.1° C. −3.9 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 603.6° C. −3.9 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 705.4° C. −3.8 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 804.6° C. −3.7 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 904.8° C. −3.6 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 1005.3° C. −3.5 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 1105.3° C. −3.3 Test Example 80 Ba₅Lu₂Al₂ZrO₁₃ 1204.3° C. −3.0 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.075) 355.85° C. −3.7 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.076) 405.85° C. −3.3 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.077) 454.85° C. −3.0 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.078) 504.85° C. −2.7 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.079) 554.85° C. −2.5 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.080) 604.85° C. −2.3 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.081) 654.85° C. −2.1 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.082) 704.85° C. −2.0 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.083) 755.85° C. −1.9 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.084) 805.85° C. −1.8 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.085) 855.85° C. −1.7 Test Example 82 Ba₇Nb_(3.85)W_(0.15)MoO_(20.086) 905.85° C. −1.6 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.125) 355.85° C. −4.0 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.126) 405.85° C. −3.7 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.127) 454.85° C. −3.3 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.128) 504.85° C. −3.1 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.129) 554.85° C. −2.8 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.130) 604.85° C. −2.6 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.131) 654.85° C. −2.4 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.132) 704.85° C. −2.3 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.133) 755.85° C. −2.2 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.134) 805.85° C. −2.1 Test Example 83 Ba₇Nb_(3.75)W_(0.25)MoO_(20.135) 855.85° C. −2.0

For all of Test Examples shown in Tables 16 to 32, the electrical conductivity represented by log [σ(Scm⁻¹)] in the temperature range of 280 to 909° C. was within the range of −7.0 to −1.0. Among these, for example, Test Example 32 exhibited high electrical conductivity at a low temperature of −3.4 to −2.0 at 306 to 606° C.

Calculation Example

For Ba₇Nb₄MoO₂₀, a structure in which a part of Nb was substituted with another element was designed, and the a-axis length, b-axis length, c-axis length (Å), α-angle, β-angle, and γ-angle (o) of the lattice constants were obtained by calculation.

Test Examples 84 to 152, Tables 33 to 36

TABLE 33 Lattice constant Composition a[Å] b[Å] c[Å] α[°] β[°] γ[°] V[Å³] Test Example 84 Ba₇Nb₃AgMoO 5.9399 5.9399 16.7929 90 90 120 513.1154 Test Example 85 Ba₇Nb₃AlMoO₂₀ 5.9004 5.9004 16.7432 90 90 120 504.8147 Test Example 86 Ba₇Nb₃AtMoO₂₀ 6.0105 6.0105 16.8606 90 90 120 527.5049 Test Example 87 Ba₇Nb₃AuMoO₂₀ 5.9405 5.9405 16.7767 90 90 120 512.7134 Test Example 88 Ba₇Nb₃BeMoO₂₀ 5.9043 5.9043 17.1673 90 90 120 518.2808 Test Example 89 Ba₇Nb₃BiMoO₂₀ 5.9920 5.9920 16.8362 90 90 120 523.5022 Test Example 90 Ba₇Nb₃BrMoO₂₀ 5.9449 5.9449 16.8107 90 90 120 514.5259 Test Example 91 Ba₇Nb₃CaMoO₂₀ 6.0137 6.0137 16.8462 90 90 120 527.6174 Test Example 92 Ba₇Nb₃CdMoO₂₀ 6.0044 6.0044 16.9154 90 90 120 528.1425 Test Example 93 Ba₇Nb₃CeMoO₂₀ 6.0494 6.0494 17.0041 90 90 120 538.9045 Test Example 94 Ba₇Nb₃CoMoO₂₀ 5.8816 5.8816 16.7377 90 90 120 501.4317 Test Example 95 Ba₇Nb₃CrMoO₂₀ 5.8835 5.8835 16.7383 90 90 120 501.7814 Test Example 96 Ba₇Nb₃CuMoO₂₀ 5.9062 5.9062 16.7619 90 90 120 506.3652 Test Example 97 Ba₇Nb₃DyMoO₂₀ 6.0139 6.0139 16.8020 90 90 120 526.2740 Test Example 98 Ba₇Nb₃ErMoO₂₀ 6.0051 6.0051 16.7818 90 90 120 524.0937 Test Example 99 Ba₇Nb₃EuMoO₂₀ 6.0274 6.0274 16.9215 90 90 120 532.3955 Test Example 100 Ba₇Nb₃FeMoO₂₀ 5.8833 5.8833 16.7350 90 90 120 501.6530 Test Example 101 Ba₇Nb₃GaMoO₂₀ 5.9337 5.9337 16.7641 90 90 120 511.1718 Test Example 102 Ba₇Nb₃GdMoO₂₀ 6.0233 6.0233 16.8252 90 90 120 528.6394 Test Example 103 Ba₇Nb₃GeMoO₂₀ 5.9023 5.9023 16.7687 90 90 120 505.9081

TABLE 34 Lattice constant Composition a[Å] b[Å] c[Å] α[°] β[°] γ[°] V[Å³] Test Example 104 Ba₇Nb₃HgMoO₂₀ 5.9874 5.9874 16.8641 90 90 120 523.5637 Test Example 105 Ba₇Nb₃HoMoO₂₀ 6.0093 6.0093 16.7906 90 90 120 525.1054 Test Example 106 Ba₇Nb₃IMoO₂₀ 5.9893 5.9893 16.8244 90 90 120 522.6582 Test Example 107 Ba₇Nb₃InMoO₂₀ 5.9935 5.9935 16.8234 90 90 120 523.3607 Test Example 108 Ba₇Nb₃IrMoO₂₀ 5.9210 5.9210 16.7764 90 90 120 509.3578 Test Example 109 Ba₇Nb₃LaMoO₂₀ 6.0475 6.0475 16.9785 90 90 120 537.7646 Test Example 110 Ba₇Nb₃LiMoO₂₀ 5.9735 5.9735 16.8486 90 90 120 520.6503 Test Example 111 Ba₇Nb₃LuMoO₂₀ 5.9926 5.9926 16.7608 90 90 120 521.2621 Test Example 112 Ba₇Nb₃MgMoO₂₀ 5.9622 5.9622 16.7701 90 90 120 516.2773 Test Example 113 Ba₇Nb₃MnMoO₂₀ 5.8856 5.8856 16.7469 90 90 120 502.3922 Test Example 114 Ba₇Nb₃NaMoO₂₀ 5.9690 5.9690 16.7910 90 90 120 518.0919 Test Example 115 Ba₇Nb₃NbMoO₂₀ 5.9880 5.9880 16.8980 90 90 120 524.7378 Test Example 116 Ba₇Nb₃NdMoO₂₀ 6.0421 6.0421 16.9181 90 90 120 534.8888 Test Example 117 Ba₇Nb₃NiMoO₂₀ 5.8855 5.8855 16.7436 90 90 120 502.2851 Test Example 118 Ba₇Nb₃NpMoO₂₀ 6.0064 6.0064 16.8218 90 90 120 525.5746 Test Example 119 Ba₇Nb₃OsMoO₂₀ 5.9244 5.9244 16.7650 90 90 120 509.6000 Test Example 120 Ba₇Nb₃PMoO₂₀ 5.8411 5.8411 16.7130 90 90 120 493.8210 Test Example 121 Ba₇Nb₃PbMoO₂₀ 6.0062 6.0062 16.8558 90 90 120 526.6073 Test Example 122 Ba₇Nb₃PdMoO₂₀ 5.9240 5.9240 16.7783 90 90 120 509.9204 Test Example 123 Ba₇Nb₃PoMoO₂₀ 6.0070 6.0070 16.8671 90 90 120 527.0855

TABLE 35 Lattice constant Composition a[Å] b[Å] c[Å] α[°] β[°] γ[°] V[Å³] Test Example 124 Ba₇Nb₃PrMoO₂₀ 6.0458 6.0458 16.9520 90 90 120 536.6149 Test Example 125 Ba₇Nb₃PtMoO₂₀ 5.9252 5.9252 16.7798 90 90 120 510.1879 Test Example 126 Ba₇Nb₃PuMoO₂₀ 6.0042 6.0042 16.8270 90 90 120 525.3532 Test Example 127 Ba₇Nb₃ReMoO₂₀ 5.9247 5.9247 16.7657 90 90 120 509.6719 Test Example 128 Ba₇Nb₃RhMoO₂₀ 5.9152 5.9152 16.7801 90 90 120 508.4750 Test Example 129 Ba₇Nb₃RuMoO₂₀ 5.9179 5.9179 16.7682 90 90 120 508.5669 Test Example 130 Ba₇Nb₃SMoO₂₀ 5.9932 5.9932 17.0627 90 90 120 530.7513 Test Example 131 Ba₇Nb₃SbMoO₂₀ 5.9456 5.9456 16.7884 90 90 120 513.9662 Test Example 132 Ba₇Nb₃ScMoO₂₀ 5.9717 5.9717 16.7853 90 90 120 518.3833 Test Example 133 Ba₇Nb₃SeMoO₂₀ 5.9265 5.9265 16.7973 90 90 120 510.9378 Test Example 134 Ba₇Nb₃SiMoO₂₀ 5.8604 5.8604 16.7114 90 90 120 497.0433 Test Example 135 Ba₇Nb₃SmMoO₂₀ 6.0338 6.0338 16.8651 90 90 120 531.7507 Test Example 136 Ba₇Nb₃SnMoO₂₀ 5.9669 5.9669 16.7860 90 90 120 517.5743 Test Example 137 Ba₇Nb₃SrMoO₂₀ 6.0420 6.0420 17.0497 90 90 120 539.0294 Test Example 138 Ba₇Nb₃TaMoO₂₀ 5.9404 5.9404 16.7921 90 90 120 513.1733 Test Example 139 Ba₇Nb₃TbMoO₂₀ 6.0335 6.0335 16.8976 90 90 120 532.7175 Test Example 140 Ba₇Nb₃TcMoO₂₀ 5.9169 5.9169 16.7632 90 90 120 508.2433 Test Example 141 Ba₇Nb₃TeMoO₂₀ 5.9765 5.9765 16.8042 90 90 120 519.8019 Test Example 142 Ba₇Nb₃TiMoO₂₀ 5.9210 5.9210 16.7664 90 90 120 509.0554

TABLE 36 Lattice constant Composition a[Å] b[Å] c[Å] α[°] β[°] γ[°] V[Å³] Test Example 143 Ba₇Nb₃TiMoO₂₀ 6.0148 6.0148 16.9154 90 90 120 529.9799 Test Example 144 Ba₇Nb₃TmMoO₂₀ 6.0010 6.0010 16.7754 90 90 120 523.1813 Test Example 145 Ba₇Nb₃UMoO₂₀ 6.0076 6.0076 16.8261 90 90 120 525.9239 Test Example 146 Ba₇Nb₃VMoO₂₀ 5.8923 5.8923 16.7503 90 90 120 503.6431 Test Example 147 Ba₇Nb₃WMoO₂₀ 5.8644 5.8644 16.7512 90 90 120 503.6431 Test Example 148 Ba₇Nb₃XeMoO₂₀ 6.0688 6.0688 16.7427 90 90 120 534.0269 Test Example 149 Ba₇Nb₃YbMoO₂₀ 6.0037 6.0037 16.8261 90 90 120 525.2420 Test Example 150 Ba₇Nb₃ZnMoO₂₀ 5.9552 5.9552 16.7849 90 90 120 515.5207 Test Example 151 Ba₇Nb₃ZrMoO₂₀ 5.9782 5.9785 16.7934 90 90 120 519.7711 Test Example 152 Ba₇Nb₃YMoO₂₀ 5.9985 5.9985 16.7934 90 90 120 523.3099

According to the calculation examples, the optimized structures of the compounds having the compositions of Test Examples 84 to 152 retain the crystal structure of the original hexagonal perovskite-related compounds, indicating the possibility that these compositions can be synthesized. Similar to Test Examples 1 to 83, it is considered that these compositions also exhibit excellent characteristics in, for example, electrical conductivity at a low temperature when used in a solid electrolyte.

INDUSTRIAL APPLICABILITY

According to the solid electrolyte, and the electrolyte layer and battery using the solid electrolyte of the present invention, a solid electrolyte having high electrical conductivity even in a low-temperature region, an electrolyte layer, and a battery using the solid electrolyte can be obtained. The solid electrolyte according to the present invention can also be used in a solid oxide fuel cell, a sensor, a battery, an electrode, an electrolyte, an oxygen concentrator, an oxygen separation membrane, an oxygen permeation membrane, an oxygen pump, a catalyst, a photocatalyst, an electric/electronic/communication device, an energy/environment-related device, an optical device or the like. 

1. A solid electrolyte comprising a hexagonal perovskite-related compound, wherein the compound is a compound represented by the following general formula (1): Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (1) wherein, in the formula (1), M is a cation of at least one element selected from the group consisting of Ag, Al, At, Au, Be, Bi, Br, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, I, In, Ir, La, Li, Lu, Mg, Mn, Na, Nb, Nd, Ni, Np, Os, P, Pb, Pd, Po, Pr, Pt, Pu, Re, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Tc, Te, Ti, Tl, Tm, U, V, W, Xe, Y, Yb, Zn, and Zr; and a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −1.1 or more and 1.1 or less, y represents a value of 0 or more and 1.1 or less, and z represents an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, provided that in the formula (1), |x|+y≥0.01 is satisfied.
 2. A solid electrolyte comprising a hexagonal perovskite-related compound, wherein the compound is a compound represented by the following general formula (2): Ba_(7-α)Nb_((4−x-y))Mo_((1+x))M_(y)O_((20+z))  (2) wherein, in the formula (2), M is a cation of at least one element selected from the group consisting of W, V, Cr, Mn, Ge, Si, and Zr; and a represents a Ba deficiency amount and represents a value of 0 or more and 0.5 or less, x represents a value of −1.1 or more and 1.1 or less, y represents a value of 0 or more and 1.1 or less and satisfying |x|+y≥0.01, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less.
 3. A solid electrolyte comprising a hexagonal perovskite-related compound, wherein the compound is a compound represented by any of the following general formulas (3) to (13): Ba₇Nb_((4−x))Mo_((1+x))O_((20+z))  (3) wherein, in the formula (3), x represents a value of −1.1 or more and −0.01 or less or 0.01 or more and 1.1 or less, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less; Ba₇Nb_((4−y))MoM_(y)O_((20+z))  (4), wherein, in the formula (4), M is a cation of at least one element selected from the group consisting of V, Mn, Ge, Si, and Zr; and y represents a value of 0.01 or more and 1.1 or less, and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less; Ba₇Nb₄Mo_((1−y))M_(y)O_((20+z))  (5) wherein, in the formula (5), M is a cation of at least one element selected from the group consisting of V and Mn; and z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less; Ba₇Nb_((4−y))MoCr_(y)O_((20+z))  (6) wherein, in the formula (6), z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less; Ba₇Nb_((4−y))MoW_(y)O_((20+z))  (7) wherein, in the formula (7), z is an oxygen non-stoichiometry and represents a value of −2.0 or more and 2.0 or less, and y represents a value of 0.01 or more and 1.1 or less; Ba₃W_((1−x))V_((1+x))O_((8.5+z))  (8) wherein, in the formula (8), x represents a value of −0.8 or more and 0.2 or less, z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less; Ba₃Mo_((1−x))Ti_((1+x))O_((8+z))  (9) wherein, in the formula (9), x represents a value of −0.3 or more and 0.1 or less, z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 0.3 or less; Ba₇Ca₂Mn₅O_((20+z))  (10) wherein, in the formula (10), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less; Ba_(2.6)Ca_(2.4)La₄Mn₄O_((19+z))  (11) wherein, in the formula (11), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less; La₂Ca₂MnO_((7+z))  (12) wherein, in the formula (12), z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less; and Ba₅M₂Al₂ZrO_((13+z))  (13) wherein, in the formula (13), M represents any of Gd, Dy, Ho, Er, Tm, Yb, or Lu; and z is an oxygen non-stoichiometry and represents a value of −1.0 or more and 1.0 or less.
 4. The solid electrolyte according to claim 1, wherein x is 0.06 or more and 0.30 or less.
 5. The solid electrolyte according to claim 3, wherein the compound is a compound represented by the general formula (3), and x is 0.06 or more and 0.30 or less.
 6. The solid electrolyte according to claim 4, wherein x is 0.19 or more and 0.21 or less.
 7. The solid electrolyte according to claim 2, wherein in the compound, an a-axis length, a b-axis length, a c-axis length (Å), an α-angle, a β-angle, and a γ-angle (o) of a lattice constant are 5.35<a<6.56, 5.35<b<6.56, 15.14<c<18.52, 89<α<91, 89<β<91, and 119<γ<121, for the formula (2), respectively.
 8. The solid electrolyte according to claim 3, wherein in the compound, an a-axis length, a b-axis length, a c-axis length (Å), an α-angle, a β-angle, and a γ-angle (o) of a lattice constant are in the numerical range of 5.35<a<6.56, 5.35<b<6.56, 15.14<c<18.52, 89<α<91, 89<β<91, and 119<γ<121, for the formulas (3) to (7), 5.23<a<6.4, 5.23<b<6.4, 18.96<c<23.19, 89<α<91, 89<β<91, and 119<γ<121, for the formula (8), 5.34<a<6.54, 5.34<b<6.54, 19.12<c<23.39, 89<α<91, 89<β<91, and 119<γ<121, for the formula (9), 5.23<a<6.41, 5.23<b<6.41, 46.23<c<56.51, 89<α<91, 89<β<91, and 119<γ<121, for the formula (10), 8.85<a<10.83, 5.11<b<6.26, 14.07<c<17.21, 89<α<91, 100<β<104, and 89<γ<91, for the formula (11), 5.05<a<6.19, 5.05<b<6.19, 15.57<c<19.03, 89<α<91, 89<β<91, and 119<γ<121, for the formula (12), and 5.35<a<6.55, 5.35<b<6.55, 22.23<c<27.18, 89<α<91, 89<β<91, and 119<γ<121, for the formula (13), respectively.
 9. The solid electrolyte according to claim 1, wherein the solid electrolyte is a solid electrolyte used as an oxide ion (O²⁻) conductor and is used under a temperature condition of 300 to 1200° C.
 10. The solid electrolyte according to claim 1, wherein the solid electrolyte has an electrical conductivity represented by log [σ(Scm⁻¹)] of −7 or more when measured at 300° C.
 11. The solid electrolyte according to claim 1, wherein the solid electrolyte is a solid oxide fuel cell (SOFC), a sensor, a battery, an electrode, an electrolyte, an oxygen concentrator, an oxygen separation membrane, an oxygen permeation membrane, an oxygen pump, a catalyst, a photocatalyst, an electric/electronic/communication device, an energy/environment-related device, or an optical device.
 12. The solid electrolyte according to claim 1, wherein the solid electrolyte is used for an electrolyte layer used in a solid oxide fuel cell (SOFC), a sensor, an oxygen concentrator, an oxygen separation membrane, an oxygen permeation membrane, or an oxygen pump.
 13. An electrolyte layer comprising the solid electrolyte according to claim
 1. 14. A battery comprising the electrolyte layer containing the solid electrolyte according to claim
 13. 15. The battery according to claim 14, wherein the battery is a solid oxide fuel cell (SOFC). 